Its interesting to me that while Miura show's us a clear change in the outward appearance of the humans (in which they all look like they've entered astral projections of themselves ala magic) we don't see any apostles? Are they going to change?
Well it might not be an actual change per se. More like they're washed over by the wave of light and see things through their spiritual selves because of it. I wouldn't expect people to constantly look like that from now on if I were you.
I thought of that too because it would be easy to lose him in the similarly ragged draping around Skull Knight's horse, would be really cool, and mostly because we still don't know what the hell he was doing up there, other than observing. That said, Rakshas being able to pull that off without SK knowing seems as far-fetched to me as Skully hitting Femto completely unawares: unlikely to succeed.
Yeah, as much as I like the idea, the way I envisioned it in the former thread was more like he'd do it in the midst of some intense action, and even then it wasn't the likeliest thing. Yet, since we didn't see SK leave, it remains a possibility that Rakshas could have somehow managed to jump through a portal after him.
Anyway, I'm curious to see what Rakshas role in this is; was he shown just to establish that he was in fact there, serving as a bodyguard, or has he yet to complete his duty, whether that involve Skully, Daiba, or whatever?
There's also the possibility that he was just observing, maybe even for personal reasons (and I guess Griffith wouldn't really care all in all). It'd be cool to see him get Daiba on the way down, though.

Heh. Perhaps before Hanafabuku can work his magic, Rakshas will lop his head off...
Somehow I doubt that.
It seems to me that the necessary components for this reaction to occur are as follows: a twice transformed human (ganishka), a deep connection to the spiritual realm (provided by the beherit sword), and probably the merging of the realms
You make this sound very complicated when it's really very simple. Ganishka was filled with power he took from the abyss. SK's sword can cut through the worlds. It cut through Ganishka (beyond the mere physical level) and unleashed the huge power he had stored inside his giant body. That's it. Whether the merging of the worlds played a role or not is unknown.
the reincarnation of Griffith
Since we can be as nuanced as possible, allow me to say that this formulation is a bit misleading. The old Griffith ceased to exist when Femto was born. He was transformed, and he was given a new name for a reason: because while he's the same in some ways, he's also fundamentally different. What happened at the end of volume 21 was that Femto came into the world and was embodied in flesh. It's not the old Griffith that came back after spending a while wandering as a spirit. It's a different being, despite the similarities. Nuanced enough for you?

I guess my question is: why did this happen?
To change the world. That fits the God Hand's agenda, and beyond them, the Idea of Evil's plans. How or why, we don't know yet.
The way i currently see it is that when a human (such as ganishka) becomes an apostle their form becomes more closely tied to the spiritual world, i'm guessing more closely than Guts or Casca (where the brand puts a person)...so beyond the interstice? Apostles are certainly closer to the abyss.
That's a confusing way to put it, especially since you use vague words here ("form"). When someone becomes an apostle, his spiritual self is changed. Infused with evil. In turn, that changes his corporeal body. And when an apostle dies, as his soul departs and joins the Vortex, his body reverts to its normal self. The key to understand things here is that what is empowered is not the corporeal. It only reflects the changes that take place on a deeper level.
As for being more closely tied to the astral world than normal people, well yes, certainly they are. However, they are not necessarily beyond the Interstice. They exist both in the material and spiritual worlds, just like branded people. Finally, when it comes to the Abyss, you shouldn't assume too many things. Closer to it than branded people or not, they are still not that close, and it doesn't matter much in the end.
All in all, keep in mind that we don't know too many things about these matters.
When Ganishka put himself inside the apostle's womb he, obviously, changed again. I'd say that his connection to the abyss was far stronger and that level of connection to this realm is clearly represented in not only the difference in his form from other apostles, but also in his overall consciousness and awareness of the world around him.
"Apostle's womb"? What a misnomer. When did that become an acceptable name? It's just apostles sewn together and filled with amniotic fluid. Let's not be too creative about it. Anyway, when Ganishka transmutated again, he became something beyond apostles (and it's useless to compare him to them anymore at this point). There is no need to search for vague, unclear and unsure explanations when what he says sums it all up perfectly: "I reached the abyss of the evil world, and have gained power..."
So yes, obviously his connection to the abyss was strong since he took power directly from it. And your use of words like "realm" is confusing. We are aware of 3 different worlds in Berserk: Corporeal, Astral, Ideal. That's all.
Ganishka's initial remarks about reaching the abyss and drawing up its power are somewhat questionable in my mind. That is to say, i'm not entirely sure he entered the abyss, where the Idea resides but entered an area beyond the scope of the Eclipse ceremonies for certain (the vortex of souls?).
The problem here is to define what's part of the abyss and what isn't. Where it starts and ends. If you figure the abyss is the hole in the middle of the Vortex of Souls, then wouldn't reaching the Vortex of Souls also mean reaching the top of the abyss? I believe that trying to define places and apply limits to them by ourselves without having a solid basis for it is not a good thing. For example, "the scope of the Eclipse ceremonies" doesn't really mean anything. We know absolutely nothing about the place where Griffith's Occultation ceremony happened. And we know even less about the abyss ("abyss" being in itself a rather generic term that could be applied to different things in different contexts).
As for the Vortex of Souls, it isn't even a layer of the astral world in itself (just an area of the ocean of souls that exists at the bottom of the astral world), and probably shouldn't be defined as being before or after such and such location at this point. It's a tad subtler than that. In any case, we've just seen Ganishka opening up and what we've seen inside him tends to corroborate what he told Daiba.
I doubt his descent into the abyss because i'm guessing that anyone who would travel to such an area would meet the Idea and that he would have remarked on it in some manner. But this is not necessarily so.
Like you say, it is not necessarily so. In fact, since we know practically nothing about the Ideal part of the world, the Abyss, or the Idea of Evil, I would say that it's a pretty bad idea to assume what should or shouldn't happen in there. One thing we know is that the "ocean" that is down there is vast. Extremely so, from what we've seen of it.
To me, it seems like his intact apostle body, combined with his strong will, allowed him to keep some semblance of form and ego upon coming in contact with the vortex of souls to the point where he even houses it within himself. His desire for the light could be contrasted with the evil spirits desire for bodily warmth?
What is "intact apostle body" supposed to mean here? I just don't see how it's related at all. Ganishka, as an apostle having some magical knowledge, used the "artificial beherit" he and Daiba had created to take power for himself directly from the source. Not necessarily "housing" the
whole Vortex of Souls within himself, but maybe having leeched some of it.
Also, are you associating the specters that harass Guts at night with the souls from the Vortex? Because they're two different things.
(beherits seem to be tied to the abyss given their point of creation: The Idea)
The Idea of Evil is indeed the creator and master of the beherits, however their creation process isn't detailed aside from what Griffith sees as he descends towards the abyss in volume 13.
a general overlap of the realms/ weakening of the Physical realm (Griffith's ability to perform miracles and make people believe in the impossible seems to be contributing to this in addition to his presence)
We know that the worlds are merging. "The physical realm weakening" is something you made up.
I base such speculation on the similarities to the abyss (see: lost episode) and pg 10-11 of 304 ( where ganishka is being replaced by a gigantic hole)
Then why do you think Ganishka was mistaken when he said he went to the abyss?
if that's the case...then it seems almost as if one world is being bypassed to bring the abyss closer to the physical realm. Given the way we've seen the beherit sword work in the past, as in Qliphoth, it seems likely that the physical realm is being pulled into the astral realm, thus helping to explain the astral like forms all the people are seen to take. Alternatively, it could be the other realms pouring into the physical realm (almost as if spiritual concentrations had properties akin to pressures of science).
The abyss isn't a "world". It's just an area at the bottom of the astral world. You're contradicting yourself in your own paragraph here. Anyway, what's hard to get in "the worlds are merging"? Why the need to relate it to pulling or pouring? Anyhow, if I had to choose between the two, right now I'd rather say something is spilling into the world.
What happens to Beast!?
Who or what is "Beast"?
do you think we will see some "good" spirits making appearances now that the worlds are becoming merged?
It's very possible. One thing I've been wondering about is whether the God Hand can fully control what's happening or not. This new world with different principles could also mean that they will be more vulnerable in a way.
What the hell will SK do now? Will his fighting spirit be broken after this turn of events?
Who knows. But I don't think that'll stop him or even depress him (is he even capable of being depressed?). It'd be more his style to digest what happened and then think of a way to succeed the next time. Look at his reaction when his attack failed: he just factually commented on what Femto did.
What does the preview text on page 21 say?
Nothing important. Check the first posts I made in this thread and you'll have most of it.