I have been analyzing XUL for quite a while with a view to perhaps redeveloping my software using it. Looks like I have been beaten to the punch – have a look at Elixon, the end result of 3 years of development. I have corresponded with Daniel the core developer who informs me that it will be a commercial app to begin with – but may eventually become Open Source. If it does it will be a great help to the community. Even so, it is a great example of what remote XUL is capable of.