I'm expecting the worst. No regional pricing but region locking implemented anyway. And a bad exchange rate to boot. That's what GMG did when they transitioned to INR earlier this year. A $60 game would cost $70ish on GMG. On top of that they disabled the VIP section for us and coupons don't work either. So basically the site became instantly useless. I hope that doesn't happen to Steam
That would be extremely disappointing, and I doubt Valve would have gone ahead with the change.
Take a look at CS:GO pricing:
So far, all of the regional pricing implemented after Euros and Pounds have made games cheaper, not more expensive than USD. Edit: Except Yen, very often, and there's a lot of locked games, specially japanese games.
Of course, there's the random dev that changes the presets *cough* Capcom *cough*, but they're still priced about the same as the USD price at worst.