I'd be very interested in a osTicket (www.osticket.com) or osTicket-like add-on.
Should be fully controllable with xenForo's permission system for support team members, ticket submitting and administrating through xenForo.
Drop me a private message with an offer if you're interested, and we'll talk
I'm sure there would be quite a few admins prepared to split the cost on this - I'd be more than prepared to do this. Such a system would be a god send for us, even to the point that I've been thinking about developing a system to do it!
But time as always is the Enemy, if there's a chance to get one as an XF addon, I'd prefer that.
I'd suggest there would be a good market for one too.