Yeah, I think that Batman should be left fallow for a while now. We've just had a hugely promoted final movie in a generally well-received trilogy, so this version will be in the public consciousness for a good few years. When the memory of these films has faded somewhat, the appetite will be there for a new take on the character. And whether they bring him back via a new Bat-series or via a JLA film, I don't think there's ever been a real need to dwell on his origin - a silent, black 'n' white flashback to the Waynes' murder (ala Year One) and a brief mention of travelling the world in the intervening years, training his mind and body to fulfil his childhood vow, is really all that's required. As for whether it could top Nolan's trilogy, I don't see why not - as good as these past three films have generally been, I still think the '90s animated series is the best screen version of Batman we've had... (lobs metaphorical grenade into room, runs aways...)
In theory, DC have presumably got a much larger back catalogue of characters to access than Marvel (what with them having a few decades on their competitor, and not having rented out any of their golden geese characters), so they've got a lot of film options that they could try out in the meantime. As mentioned in this thread and the "next comic movie" thread, Wonder Woman deserves a decent crack - it's an instantly recognisable international icon, it could fill that "big summer blockbuster" void, and if the positive reactions to Black Widow and Catwoman this summer are anything to go by, audiences are ripe for a superheroine movie.
Other than WW, there's a bit less name recognition, so it's worth DC exploring less traditional avenues, or twists on the genre. Legion of Super-Heroes, blurring sci-fi and superhero, could work brilliantly, especially if you play up the "inspired by exploits of 21st century icons (Supes/Bats/etc)" riff. Or if we're looking at someting a bit more modest rather than a huge franchise, DC have a some great horror options (a proper Hellblazer would be fun), westerns (Bat Lash would be cool!), war (Enemy Ace, anyone? Actually, I kinda like the idea of Creature Commandoes or Unknown Soldier, but then I'm odd like that...), and more besides.