Innovative makes me think there will be some element of sci fi involved. Maybe not what we’d normally expect from the genre but some variation or melding of it with other elements. Or innovative could just be on the technical filmmaking side of things.
My guess is that his next film has a lot of scientifical stuff in it. Maybe the story of an explorer or something. Do you know the book "the swarm" by Frank Schätzing? It is a thriller about an yet unknown intelligent species living in the depths of our oceans and written from a very scientific point of view with some action elements in it. It would be quite a spectacle if it was filmed by Nolan I imagine. Filming under water etc. (No idea if that's even possible with Imax^^)