txt2tags is also very nice, I made a patch to support bbcode (-t bbcode), I attached the patch (and the test document I used) in this message.
The advantage txt2tags has over XSLT is that it's a lot easier (And still works pretty well).
Another thing I'm working on is making the guide section a wiki, I'm using
dokuwiki as a backend, I'm working on integrating it a bit with vB.
... so this will also affect things, adding new output syntax to txt2tags is fairly simply, I'm not familiar with XSLT so I can't say anything about that...