I prefer the 2D sprites that we've had in Pokemon, lately, but who knows? Having 3D Pokemon could enhance the Pokemon gaming experience in a manner that is better than we expected... More frames would be greatly appreciated, though... :)
If Nintendo had a GBA slot like the original Nintendo DS (Lite), that would be awesome. I don't know the exact specifications, but if the original GBA (SP) slot could be implemented instead (the one that plays GBA, GBC, and GB games), that would be...indescribable. :) Backwards compatibility for the whole Nintendo handheld family (excluding Game & Watch and the other 'spin-offs')? That would be impressive. (I know, kind of outdated, but I'm stuck on the Pal Park issue since I'm still stuck in Generation III, and I still have to save up for both Pokemon Platinum and HeartGold Versions, since the Generation 5 games will probably be missing several easily obtainable Pokemon from Pt and HG. Having a 3DS and still being able to do Gen_III-to-Gen_IV transfers along with the presumably upcoming Gen_IV-to-Gen_V transfers would be very convenient for me.)
Anyway, I'll keep on waiting for Generation V to roll around in full force soon enough (aside from Light-types, I'm really hoping that this is the Generation that employs more 'action' [via the announced rebirth of the series], as Junichi Masuda said he wanted to add to the series months ago...) :D
EDIT: And more Seals, please (feathers, leaves, diamonds, etc. Minor feature, but it's still a nice touch to Poke Ball animations...) Speaking of PokeBall animations, if Generation V should happen to use 3DS-exclusive features, the PokeBall animations should be smooth at least. The 3D incarnations of 'Poke Ball throwing' I've seen in Pokemon Stadium 2 and Battle Revolution have looked a bit...jilted, on occasion.