limited edition Galaxy Tab 10.1 would be getting updated to Android 3.1 in the next couple of weeks, and it looks like it will be a similar situation with the WiFi-only Xoom. Motorola has just announced that it will receive the update "within the next several weeks." It also reaffirmed that the Verizon 3G Xoom is rolling out over the air this week, so you should be receiving it soon if you haven't already. Full press release is after the break.
Update: Judging from the official Motorola support forum, it seems like a few lucky individuals may have already received the update on their WiFi-only Xoom. 3G Xoom users now also have another option besides waiting for the OTA update -- they can install it manually, as explained by Android Total.
Update 2: Motorola's officially announced that the Xoom WiFi will start getting Android 3.1 right now, though it'll roll out "in phases" so don't be bummed if you don't see yours quite yet.
[Thanks, Jake E.]