It won't happen though. MMO is against the core ideologies GameFreak has for the Pokémon games.
A spin-off MMO is plausible, but main series is not
There is. Pokémon Rumble U is a download title, sitting high on the Wii U eShop charts in Japan each week. In Japan, there are currently two series of figures out, as well, for it coming in at 200 Yen a piece, though through Gachapon Machines
The game is 1800 Yen for download, and they're selling download cards in stores so it's getting good reach in Japan. It's quite likely to be localised and I'd be surprised if we didn't get localisation confirmation during E3. The previous games in the series were huge. The first one was consistently at the top of Wii Shop Channel charts for over 2 years and the 3DS one was one of the first 3DS games to break 1 million units sold. I would provide a link to a site with more details, but the mods would kill me for doing so