Ryuuhan is a veeeery mysterious man, with deep, dark secrets. Maybe he's planning on reviving the Quincy order to oust those pestilent Shinigami he despises so.

Well, my guess is as good as any, but I'd say that he's eager to restore Ishida's powers, bestow upon him the Quincy cross, send him on his way, and be done with being a Quincy forever.