If Motorola is as good at releasing a 4G Xoom as they were at upgrading the 3G model, I wouldn't count on ever seeing one.
But Droid Life claims to have found some evidence suggesting a 4G model is on the way. Apparently the 4G Xoom is now listed on Verizon's MAP (minimum advertised price), a usually accurate hint that something's about to break out. Not only that, the same rumor further confirms that the DROID 3 is also getting ready to make its debut. As a Droid owner, I'm more pumped about the latter over the whole Xoom business—especially because I'm not expecting the 4G Xoom to bring anything new to the table other than an already built-in 4G LTE antenna. Which is saying a lot for the Droid since it's expected to be 3G-only. [Droid Life via Mobile Crunch]