Note that if you already have an account and uploads, I apologise for not recognising who you are but you're still welcome to bug me if there's anything I can do to help :)
Having a tool that would take a PCRE (or some subset of the language), apply some constraints on repetition operators (like *->{0,2}, +->{1,2}) etc., spit out a deterministic list of values (don't care how long so long as it's reasonably finite) would be extremely powerful for software testing. Even the rather limited capabilities in REX have helped me fix some invalid assumptions I was making about valid inputs.
It's always seemed strange to me that regular expressions are described in the literature as string generators, yet I've pretty much only ever seen them used as string acceptors in practice in the form of a predicate (s in set <REGEX>?).