That's a difficult question.
1) As XWiki uses several library, I'm not sure that it
really make sense to offer dual license. As I don't
know the license used for these library (hibernate,
etc) I can't have an idea about that.
2) Switching to ASL ou LGPL license would be better if
you want XWiki to spread (as Cameron said), it would
make it harder for XPernet to make money out of XWiki.
So it's difficult balance.
Whatever your decision, my contribution is so small
that I'll agree with it.