Some higher up Pokemon Go designer at Niantic has said they plan to only allow trading in close proximity so all the talk of global trade is unlikely...
It would probably ruin the game if they allow global trading (spoofers win),
In the promo trailer, there was also trading shown, but it was an in person which is where they are probably planning to head IMO...
That said, I probably wouldn't bother trading with random people since it's a hassle and unlike cards in the TCG, you NEED certain cards to make the deck work while in POGO, not even having a Dragonite and I do plenty fine...