Might not be what you are looking for, but maybe ...
If you call xslt from within xmlsh (which uses Saxon)
then you can call XQuery from any xpath expression vi the xmlsh:eval() function.
Perhaps, this is a dumb question but all of the examples I've seen for using xquery are either from the command line or from java. I haven't seen any examples from within xslt. I could probably use xsl:function but was wondering about xquery. If it's possible, it would be great to see an example. Also, does xsl:function come with HE or would I need PE or EE?