Trust me when i say that the ball is in Motorola's court and not Sprint. There is an internal memo/directive that was delivered and documented over in xda that says Sprint will service any rooted sprint phone. Although alot have not gotten this memo and don't know about it, but the fact remains it has been issued.
So if Sprint is now allowing rooted devices to be serviced, then there is no reason why Sprint would say to Motorola we won't allow it. That leaves Motorola to fulfill their end of the deal.
TS