The main problem that I see is what happens when one tries to unify two conditionally bound objects? Should a junction be the result? Should the unification fail because we have nothing real to bind to? Should they only be allowed to unify iff they are identical?
Which leads me to wonder if Perl6's any/all
will address this space, either by default or via straightforward extension. (Or, for that matter, if Perl6's rules will be able to. I would assume they can operate on structures, not just on text source...)