According to the announcement of Windows 6.5 every device that runs 6.5 will have a dedicated Windows button, so my guess is that we won't see an official update for any of this or last generation's phones (Vogue, Mogul, Diamond, Pro).
Source Engadget:
http://www.engadget.com/2009/02/16/l...ss-conference/ look at the 3:57PM comment.
Edit: Also, why would Sprint upgrade an old phone hen they could limit the new hotness to one of their new phones?