Are we back in a scenario where the AT&T and T-Mobile models don't work on Verizon or Sprint, but the latter two work on the former two (apart from LTE Band 30)? Why can't Apple just release a single phone that works on all?
I'm not sure why they chose to segment the market arbitrarily, but the CDMA model should work on all carriers. The towers should recognize that the device doesn't support band 30, and should assign those devices a different band, just like they would if it were an older model of iPhone.
Even better, because the towers can dynamically balance band usage, the new devices should tend to end up on band 30, freeing up spectrum in the lower bands for devices that don't support it. So unless you just happen to be in a cellular dead zone where you can't see any towers on any other bands for some reason, not having band 30 on your phone shouldn't have much impact, just as long as there's a high enough percentage of devices that do have band 30 support.