vNext Issue: Why did intersection fail?

The current Framework spec says that the result of intersection is zero 
or more compatible policy alternatives.  If the intersection fails, 
there are zero compatible alternatives but there is no way to indicate 
why the intersection failed.  (If more than one alternative intersected 
we are in the space of issue "Which Policy Alternative was Selected" 
http://www.w3.org/Bugs/Public/show_bug.cgi?id=3639 which was marked 
vNext and "won't fix".)

We have had customers ask for feedback of the form "these policies are 
not compatible because Assertion X does not appear in both policies" or 
"these assertions may be compatible but, unfortunately, have different 
namespaces".  Thus, some form of feedback on why policies are not 
compatible would  be very useful.

Perhaps this is part of negotiation: 
http://www.w3.org/Bugs/Public/show_bug.cgi?id=3616
-- 
All the best, Ashok