I don't think there's a technical problem. Xenoblade Chronicles was on Wii and the Wii U has much more RAM and storage space.

The biggest problem would be the production costs of such a big project.

I, for one, would hate a Pokemon MMO. 

I like forging my own story in the game, I don't need random battles from other players ruining my day. Pokemon should always have a seperated single-player and multiplayer mode in game, and I hope they keep that system. Plus any kind of MMO requires extra money to stay afloat, and the only method of geting that money that isn't free-to-play is a subscription.

why? why the originals? there are many pokemon from 152-721 that are better than the originals :-/

Amen. 

the biggest super computer couldn't do what you want.

This.

Some are fine but if it comes at the cost of having the ones that are attrocious than no thanks.

Xenoblade isn't nearly as big as this game would be. There aren't 700+ different unique monsters in Xenoblade.

That's entirely subjective, and no real Pokemon fan think like that, and therefore wouldn't be the audience for this game anyway.

Fifth gen was bad, but most of the other Pokemon from the other gens are great. Third and sixth gen in particular have some awesome designs. 

I think we need to get past nostalgia and realize that the newer games are eons better than the originals.