I was actually relatively suprised when throughout the whole of the DS's lifetime there wasn't a single full-fledged 3D Pokemon game. It's not like they "couldn't" create one - at the end of the day, there are only whole "2" models on-screen during a fight, *surely* the DS has enough RAM to carry that much. Even the characters wouldn't have to be so diversly different, some texture work would do wonders.
If Monster Rancher could do it then I don't see why Pokemon wouldn't work out.
check my post above, Dinosaurs Clash of Giants, Drone Tactics (Konchu Wars), Zoids DS (jap) and even some really really fucking old DS beetle fighting games (jap) had this "3D" style.
its the fools and tools that don't care and go herp derp over a pokemon game because "its pokemon" and "its new" that makes Nintendo lose interest in further improvements.
why improve something when you will still make money?