I'm currently working thru the Udacity Self-Driving Car Engineer nanodegree; as a part of the first term one of the projects used a Unity3D-based simulator to train a CNN to drive a vehicle.
It would be nice to have a more generalized simulator for this kind of work, to be able to simulate potentially more accurate environments (off road, especially). I could also see interesting work being allowed for underwater ROV environments as well...
As it is, I have considered (for an off-road and more general use) re-tasking TORCS or Trigger Rally (though after just doing some research, it seems like there are ton of these simulators - so maybe one more isn't necessary).
Still - I'm curious whether other environments and vehicles are being considered...
EDIT: It looks like Udacity recently open-sourced their simulator (one thing I have noticed about this course is that sometimes they do things, but don't let the students know about it - that, or maybe I've just been too focused on my work to notice, which is a very real possibility!)