Well obviously noone who knows is likely to tell you anything, but it seems like Apple would benefit most from launching desktop systems first and Xserves second. Since it is not likely that they share very many components, Apple probably does not have enough engineering power to launch both close together. If I were to guess, I'd say the Xserve will be the second line Apple updates, and that it won't happen for a few months.
Hmmm, why am I here, I should just go to bed and stop twiddling around. 🙂 Lots of reading tomorrow, I predict.