There are several things wrong with that picture that absolutely makes it fake...
1) The Wi-fi logo is on the DS logo, and not at anytime, has any logo occupied the NDS logo.
2) As far as I have seen, whenever a Pokemon is on the front of a Pokemon game, they retain all of their colors (even back in the RBGY days), and have some sort of background/aura coming out of them, though they still retain their normal colors.
3) It always shows the Pokemon's whole body on the cover of a Pokemon game (do not include the GCN versions).
4) Why would they release GSC so soon after just barely releasing DP? The remakes of Red and Green weren't even released until about 2 years later (In Japan, RS came out in 2002, and I believe the RG remakes came out in 2004.)
5) It so totally looks like it was PSed!! The Aura seems to be randomly everywhere, whereas, the aura (not the background from the RBGY days) from other games usually seems to be radiating from the Pokemon itself, while not usually touching it.
As much as I wish something like this would happen, it is highly doubtful for numerous reasons, including the fact people would rather see Sinnoh and Hoenn Pokemon in Brawl rather than a Johto Pokemon (which is why Pichu is on the 'to take out of Brawl' list and was an advertisement for 2nd generation), and even Pokemon.com itself said the odds of it ever appearing are very slim.