POKEMON TROZEI 2!!!!
RS3DS OMG OMG OMG!!
Hmm...there are a lot of things that this as-of-now unidentified game could turn out to be. RS3DS and/or Pokemon Gray are a bit too early, considering BW is relatively recent. Then again, we got wind of BW before HGSS was even released in the United States... New Pokemon Mystery Dungeon games are also a possibility. I'd be more inclined to think that it's possibly the 3DS game or the Wii game that Satoru Iwata hinted at earlier...likely the "Pokemon XD" of Generation 5.
Might this also be an announcement for Pokemon Snap 2 on the Wii? :D It might even be a Pokemon TCG game, given the recent developments of Pokemon TCG Online.. Even more surprisingly, it might be the announcement of a brand new Pokemon side series game that's unrelated to any of the current spinoffs!
But yeah...either "Wii XD", the unlikely Gray or RS3DS, another Mystery Dungeon entry, or an entirely new spinoff are my guesses.
EDIT: I can't tell whether Dengeki Nintendo DS has started 3DS gaming coverage yet, so I'm led to believe that the likelihood of a DS game is better, although the magazine apparently covers Wii games as well... If there's no 3DS coverage yet, a DS game has more probability than a Wii game. Otherwise, it's pretty much a toss-up between the three, with "DS game" still having somewhat of an edge.