I wondered about that too. We were looking for a framework to use w/ Se2 / WebDriver and Selenesse was clearly out of date. We did look at Xebium, now that you say it's unstable I'm glad we didn't use it! So we gave up trying to do something from FitNesse.
We had already tried Geb (using Groovy and JUnit), didn't like the test result reporting. Now we're trying Robot Framework, awesome test result reporting.
-- Lisa