xmldsig-filter2 rationale questions

Please allow me to ask two (possibly naive) questions to understand the
rationale behind the new XML-Signature XPath Filter 2.0 draft:

1. If runtime performance is an issue, would it also be a possibility to
integrate the XQuery activities as XML-Signature transfomations?

2. If functionality like having node-set intersections and unions is an issue,
would be possible to consider additional mathematical node-set operations for a
future version of XPath? (I still consider it a work-around having to use
something like count(SET) = count(SET | ELEMENT) to test an element-in-set
relation ;-)

Best,

     Jochen