Implementing XForms XPath extension functions in a Mozilla extension?

Along the same lines as Allan but different.

XForms has XPath extension functions like avg(), instance(), etc.  So we 
are in a pickle.  Not only do we need to figure out how to get XPath to 
call into our extension when the expression evaluator runs, but our 
extension work will need access to all of the utility classes.

If we do the work in XPath to allow for Allan's dependency node stuff 
AND the work that I need to XPCOMify a lot of the stuff in XPath so that 
it can work well with extensions, would Firefox take it?  Or would we be 
better off taking the hit and shipping our own XPath (and forgo the hope 
of ever making it into the main tree)?

Your opinions appreciated.

Thanks,
--Aaron