I think adapting Black Swordsman (especially) and Lost Children would be fairly straightforward, as long as they stick to the source material. Overall I think I'd find something to appreciate even if it hadn't been that good, be it some 2D animations or new music.I really wouldn't say it's a pity. Given how terrible their adaptation of the Golden Age was, there's no reason to think they would have handled the rest of the story any better.
I can definitely see the Count segment being perfect for a movie, I don't remember how long exactly Lost Children is and I fear a movie would need to trim some stuff again. I can imagine the first two self-contained episodes of Black Swordsman being adapted as OVA episodes though, or even just have the whole BS / LC arcs adapted into an OVA series a-là Hellsing Ultimate. That would be my preferred format.And contrary to what you're implying, the Black Swordsman arc and Lost Children chapter are the two parts of the story that are best suited for the movie format. They're short, relatively self-contained and the Lost Children chapter could be produced as a "sequel" to the Black Swordsman arc without being disorienting for people unfamiliar with the manga.
As for my comment on "cinematic" and "kinetic" I was mainly referring to how they adapted the art and trimmed some dialogues in favor of random eye-candy moments as that's one aspect that I felt in particular, of course that's not all of it as you pointed out. It needs a special kind of talent to actively destroy the source material the way the trilogy did.