It wouldn't BE pokemon. It wouldn't be some cutesy kiddy bullshit.
It would have to be matured up some but not made all eXXXXXXtreme HARDCORE with half naked chicks everywhere like Tera or something, obviously. The term pokemon is just being used to describe the genre. Maybe we should be saying "Pokemon Like" in the vein of a "rogue like" so people get that we're not saying literally make a Pokemon MMO (though if Nintendo did, it would make a killing just in Japan alone). We're saying a game based around seeking out, battling, capturing, training "pets" (Note, these pets could be fucking dragons and umber hulks for all I care) to duel/compete with other players in a tourney style system would have broad appeal as long as it was handled maturely and developed properly.
The whole E-sports thing would be huge in it. You could have sponsored tourneys, duels, etc. just like the arena shit in WoW, but there would be the tactical depth of a Collectible Game because what you bring to the table in terms of pets, their levels, their skills and their elemental affinities would have a huge influence on your ability to win.
I can literally see dollar signs in front of my eyes talking about this. I know it would work. Someone in the industry just has to have the talent, balls, and comprehension for what people are looking for in a MMO style Pokemon like game to make it happen.
That's all.