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 rumour 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]