Maybe its because never read the abomination that was Hush Returns, but I can't help but feel that if you take the very basics of who Hush is as a character and use him for, say, the fourth movie giving him and entirely different story, he could be extremely interesting.
Simply take somebody with a massive hate-on for Bruce Wayne, so much so that they have dedicated everything they have into spying on him, looking into his personal life, background checks, etc. and eventually finds out that Bruce is Batman.
In an effort to destroy Bruce he creates the persona of Hush, and creates some sort of plan to destroy Batman. Heck, if late enough in the Franchise, you could almost go the route of Hush by having him employ a bunch of the known Rogues.