There are a few things that have been bothering me about certain characters and places lately:
Sonia: Does she know everything?

I guess not.

Charlotte: I want to bet she will sacrifice Anna at some point to become an apostle. Because that is the point of Anna being there. Probably when the truth about Griffith is revealed. Instead of turning against him, she will join him fully. I just feel it this way because Griffiths control over Charlotte is now absolute.
The pope: We will see his upcoming death from his point of view. And he will go abruptly from
"Finally paradise!" to
"OH SHIT!!! NOOOO!!! I NEED TO HAVE MY FLESH BAAACK!!!!!" (Two page spread of the vortex) He will be the first to see the truth. I'm already getting cold sweats thinking about it.
Falconia: I suspect it has a "true form" and we currently see a mask. Exactly like Griffith himself is. The true form will be the stuff of manga legends.

Luca: Just guessing, but a possible path her character can be taken on is her being "corrupted" by the comfortable life in Falconia. Luca functions great in terrible situations, but how will she hold up when she actually has something to lose? When it becomes clear Falconia is fake as a (huge) wedding cake, will she try to cling to it? Just a theory.
Falconia again: Could it be inspired by "Germania", the planned (but thankfully never build) Nazi megalopolis? It could be because it also was designed as a HUGE city of marble and pompousness with in the center the "Volkshalle". A humongous white dome in wich all the subjugate people of the world where to pledge their loyalty to the thousand year Nazi empire. (Goodwin etc., but I had to say it)
(Just quickly jumping in to drop some ideas)