The WiFi model for the U.S. seems to be first in all it's updates. It should be getting JB soon. Then comes the models for other territories & the U.S. cellular+WiFi models, in theory. In practice?
In the U.S., the WiFi + stock 4G model just recently (within the past month) received the green light for ICS. Given this, assuming the update is available for all users to apply, then the models in other territories should see Ice Cream Sandwich within the next couple of months (my guess), with JB a bit staggered behind that.
I've read many folks saying that the jump from ICS to JB isn't very big compared to jumps from 2.3 or 3.2 to 4.0 in terms of ensuring proper functionality, so hopefully all Xoom users will have at least ICS by year's end, with a firm promise of JB rolling out to whatever models don't yet have it by that point. And since Motorola seems to be taking an active interest in preparing the OS updates, I see no reason for anyone to miss Jelly Bean unless a carrier rejects updates for the cellular models.