You can root it, and also recover it if you manage to brick it using the Chinese ROM from the ME863 which has the same hardware as the XT860.
Only the D2g with an earlier FWs can be band unlocked, D2g with updated FW and D3 can't.
The part that control the lock is moved in a section that is untouchable because the locked bootloader.
So, for now, NO you can't use an XT 862 in GSM mode in the US. PERIOD.
If you need it, get a Milestone 3
I assume it too, but i assume also that, as usual, replacing a FW won't remove any kind of locks, btw I can't try this in first person, you need a volunteer from the US to have a 100% sure response.
(the XT883 rom can be flashed safely, and you can get back to verizon w/o any problem)
TBH mentioned (re D2G band unlock) Verizon asked Motorola to implement the ban on baseband level (not in NV settings) so it is more difficult to break (to break it you have to break the signature since radio is signed - right?)
I am assuming (since I can't try) that ban is done the same way on XT862 - inside actual radio image. Since XT883 bears different radio image, there is chance ban will not be present there.
But as you said - until we get someone in the US to try it we can't say for sure. If it works - I am sure XT883 firmware will become much more popular in the States..
Basically flash the XT883 rom, following the instructions in the related thread, and look if with that rom the GSM works in the US.
BTW seem that a an hack to unlock the D2g with the GB kernel has surfaced lately, so possibly the band unlocking for D3 is getting closer (they are basically the same phone).