I don't think Audi would switch unless they felt the rules favored petrol. What the performace of the toyota has shown is that at works run program with a petrol engine is a match, but not a vast amount better.
I did read that RML where invloved in a program for a GT3 Bentley.
If Bentley do join GT3, it means we would have Lambo, Audi and Porsche, 4 brands from the same stable all racing each other. Time for the EU to step in!
Can't see SEAT doing a GT program tbh.