Black and White are the best Pokemon games!
Also nothing can threaten Warcraft, that fight is over.
A Pokémon MMO definitely could with the right approach.
Aside from what's been mentioned in the image in the first post: make the Black and White region (no idea how that's called) available together with Kanto and you'd appeal to the newer fanbase, the hardcore fanbase that still buys every game AND the nostalgic fanbase that only played up until Silver/Gold or whatever. Then make the other regions DLC or what not and BAM, a legitimate threat in the MMO world.
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http://i.imgur.com/xBFwK.gif