The Verizon threads get old. If the iPhone ever sees another provider, it will be one of two ways:
Pre-LTE: It will be T-Mobile as the only other provider Apple might carry the iPhone. Apple will not re-engineer their device for American CDMA which is already obsolete, and fundamentally incompatible with other CDMA implementations like China's (which use R/UIM cards.) You will sooner see Token Ring ports appearing on Macbooks than you will see Apple put support for US CDMA in their devices.
Post-LTE: Who knows. This is going to be some years in the future because LTE won't just have to supersede 3G, it will have to supersede EDGE, and even GPRS in rural areas before SJ gives his blessing to an LTE based iPhone.
If I were to place bets, I would say that the iPhone will remain under AT&T unless the climate changes to mandate unlocked devices, then Apple will just sell the device at retail, and people buy it and then drop in the SIM card of their choice of provider.
Until LTE becomes prevalent, there is going to be no chance, no way, no how of a Verizon iPhone ever coming to be. Apple will not re-engineer a device and add another radio just for the US, on a band which will be not relevant in a couple years. So, it just will not happen.