Gotta catch 'em all.
I mean, I know what you're getting at and being able to trade would be great (battling will probably never be the same as the 'real' games), but would also kinda defeat the purpose of GO. There are no 'version exclusives' or anything like that. Of course there's the 4(?) region exclusive Pokémon, but I don't think online trading would be a thing. Too many people will trade hacked Pokémon with people from around the world, which could result in getting them banned. Trading will probably only be with people who are around you at that moment, which I'm perfectly fine with.
The power of Pokémon GO, as I experienced it, is the (groups of) people who go out and hunt for Pokémon. People recognizing other people as Pokémon trainers and telling 'em they just caught a rare Pokémon around the corner. People being excited because they finally caught that Pokémon they needed or wanted so bad all that time. Trading would ruin that magic. On top of that it could create dangerous situations for kids who'll go meet strangers from the internet to go trade Pokémon with.
Tl;dr: At least to me, Pokémon GO is all about catching them (all). Trading would be a nice addition to get that one last Pokémon you still need that your friend has 4 of, but it would kind of defeat the purpose of the game. Battling will probably never be the same as in the 3DS games, because... You know... They'd probably want you to buy the 3DS games if you want that.
edit: It's mid-winter in Holland right now and kinda cold. After they didn't drop it in December, I was expecting them to fully launch Gen 2 around ~June with some teases like the babies in between. I guess they are saving Gen 3 for summer then, seeing as I don't know anyone who would go out in the snow/cold just to catch some Pokémon. I think the game was huge in the summer because everyone was already outside anyway. Might as well catch some Pokémon.