1. Just go ahead and do a Batman Beyond movie!
For those who don't know, a live action version of the Batman Beyond TV show was planned after the failure that was Batman & Robin (I honestly haven't seen B&R...neither do I plan on doing it), but was scrapped in favor of a Batman: Year One adaptation, which eventually became Batman Begins. So a sort of 'spiritual sequel' would be made by a Beyond trilogy (and, although I doubt this would happen, Chris Nolan would make excellent contributions, since the series itself is pretty gritty). It would be fitting to place it right after Nolan's trilogy.
2. Reboot the franchise again.
I know I'll be hated for saying this, but maybe (just maybe) another reboot will be one of the few ways to continue the Batman legacy. But don't make it anything like the Burton/Schumacher series. And since Batman 3 is supposed to be the end of the series for Nolan, I'd be interested in seeing certain villains who haven't been on film before (such as Killer Croc and Harley Quinn), as well as reinvent villains who weren't in Nolan's trilogy but were in the older movies (like The Riddler [and having him played by Johnny Depp would be amazing...more on that later], Mr. Freeze, and The Penguin). But if they try to redo The Joker (which is inevitable), then PLEASE pay homage to Heath Ledger's spin, instead of the Nicholson clown.
3. Continue without Nolan directing?
Yes, I know if by any chance Warner Bros. decide to continue Nolan's series without Nolan himself directing, that the sequels will not be the same as its predecessors. But Nolan never ruled out his leaving the Batman saga completely. Maybe he can stay on as a producer (like how Tim Burton did on Batman Forever). However, that will likely conclude Christian Bale's not reprising his role, and possibly some of the other key figures in the franchise (Alfred, Gordon, etc) will be played by other people. This is one of the things that sunk the original Batman series, and I'd much rather not see this happen to the already perfect trilogy under Nolan.
4. Justice League anyone?
It's my understanding that Nolan's Batman and Zack Synder's Superman will stay in separate universes, but that was addressed only to a Bale/whoever Synder picks live action Batman/Superman film. MAYBE Bale can be back in the costume for a live action Justice League movie (I can smell prep for such a movie now...Green Lantern next summer, a Superman reboot, and The Flash, Aquaman, and Wonder Woman in development), which would be fantastic considering no one else played the role well enough as Bale did.
Well, those were the conclusions I've come to. If anyone has any other ideas of where the Bat-franchise should go, comment below!