I feel that Pokemon Go is very successful because of its balance of being social (via lures) and casual (there's not much of a competitive aspect to it). The collection mechanic makes it fun/addictive, like collecting anything else.
I think battling risks reducing how casual the game feels. Gyms already reduce that feeling... but you can pretty much completely ignore the gyms and just focus on collecting wild pokemon.
I think trading is going to be big. That should make the game even more social than it already is, without pitting players against each other. You're each individually working your way to collecting them all. Everyone can be a winner with this format - nobody feels like a loser or discouraged.
