So, ignoring the not possible/no advantage right now, the one thing I would say would say definitely not hinges on one thing: Is it easy to just get an adapter from thunderbolt to USB?
Cause if not, I'd say absolutely no way. Because Apple is trying to sell this phone to the masses, it tends to be also their way of introducing people to the Apple ecosystem that never experienced it before. If they put thunderbolt into it and it was not easily convertible to a USB connector, the only people they could sell it to right now is not just anyone with a Mac, but anyone with a brand new mac (shoot, at this point only those with a brand new MBP). So they would seriously limit who could actually use the phone.