Honeycomb will thrive just as Android for smartphones has. The Xoom will be replaced by upcoming tablets, just as every Android phone as been updated/outdated on the phone side of the market. The only competitive advantage any company has is the hardware and feature list, just like in the battle for the PC world where they all run Windows. Features will get better, prices will get cheaper.
The Xoom running the native Android is, as someone else mentioned, basically the G1, low sales, but a pure experience that will get updates when they come out. The choice to use or keep the Xoom vs another tablet is more or less comes down to your preference for having the latest and greatest hardware.. or version of Android. Then again, most other tablets can be rooted and updated with a little know how as well.
As to the sales figures of 100k a month so far, I'd be more concerned if that number is falling as the Wifi version is now on sale for $599 vs the $799 it started out at with the 3G model. If they maintain or gain over the 100k per month, it's all good and i"m sure we will soon see spec's for the Xoom 2. On the other hand if even with the Wifi at a lower price Moto gets blown out of the market by lower priced, better spec'd competition then your left on an island with few accessories for the device, but will still benefit from the growing Honeycomb user base.
For me that is the downside of the Android world, you can end up with a product that is forgotten about very quickly and no 3rd party vendors make cases or other items to go with your device. Hopefully Moto keeps the same form factor and simply updates things like the screen, memory, CPU etc..