you have nabbed my attention. although i doubt anyone on the forum is qualified to answer this question. if anything though, the 3d models of everything else in the pokemon game is probably the bigger challenge.
The PokÚdex 3D Pro has around 680 or so, counting extra forms, and that's around 3000 blocks of data. Just to put that into perspective, the full game Animal Crossing: New Leaf is roughly 5000 blocks. Most 3DS games (AC:NL included) are >2GB, because that's the smallest amount a 3DS card can hold. However, there are 3DS cards that can hold more. For example, Resident Evil Revelations and Kid Icarus Uprising (iirc) are on 4GB cartridges, and are also too large to be downloaded on the eShop. I assume that this will be the case for the new Pokemon game, considering all the old models+all the new models+locations+characters+animations+game engine+everything else. My fingers are crossed for XY to be available from the eShop, because it would be extremely convenient for me.