We've made a bit of a mess of this one. Kevin Conroy is working on a Batman: Arkham [Something] game here. That much we know to be true.
But after inferring this morning, in a daze of wishful thinking, that Conroy would be returning to play the Caped Crusader after all, it turns out that he won't be voicing Batman in Arkham Origins. Sorry for the confusion!
According to previews from Joystiq and IGN, Roger Craig Smith will take on the title role, with Troy Baker playing the Joker. It's not known yet what part Conroy will play in this (he's definitely working on an Arkham as per the Comic-Con panel). Of course, it's not infeasible that BOTH Conroy and Smith could be playing the role, with Conroy narrating from a future, older perspective, and Smith taking centre-stage as the more youthful protagonist.
Alternatively, Conroy could be voicing someone completely different, or appearing in Blackgate.
In any case, apologies again for the confusion. My bad.