Tommi is one of, if not the, best test driver(s) in WRC history. He has a very clear vision of how a WRC car should perform, some of it is very easily visible in the videos and pictures that have surfaced so far.
I think it would be a great mistake if he didnt take on an active roll on the testing and developing of the car.
I see it the other way around, when things start moving in 2017, with all the rallies and logistics etc, they Toyota Gazoo will have a "problem" in that Tommi cant be as active as he is now.