It really makes no sense to sell them locked anymore. In fact, they shouldn't have been sold locked to AT&T in the first place (even the subsidized ones). Because anybody who receives a subsidized phone from them is locked into a 2 year deal anyway and would have to pay a ETF to get out of it. AT&T still gets their money.
Also, I thought it was beyond ridiculous when Apple was selling unsubsidized phones for $599 that were still locked to AT&T. I'm thinking this may have been a side effect of the 'exclusivity' agreement. But now that that has run out, it doesn't make any sense to lock them.
With that said, I think they will offer a factory unlocked option from day 1. I'd be really shocked if they didn't.