The choice will also say something about how Apple views these ARM Macs: Are they iPhone-esque devices made exclusively for Apple software, or are they (relatively) open-ended computing platforms capable of booting alternate operating systems?
There is no way Apple would create a Windows driver for that custom silicon- it has always relied on AMD or Nvidia for those drivers in the past, it has no in house code base or expertise to write the requisite code in Windows and none of the silicon has been optimized for it.
(I do agree that they're more likely to just drop Bootcamp support.)
But since its 99% likely that all the other Mac's will be SoC with no Windows driver support for any of the underlying silicon, I'd find it very surprising if Apple went to the trouble just for the high end.
That said, I thing Intel Mac Pros will be a thing for a long while, even is a 256 core ARM variation came out, just to keep the pros happy until they can comfortably transition to the new stack. Apple has spent too much human capital recently on the pro team to make me think otherwise.