Well, that idea has been in my head for a long time, obviously I expected Mazda to go for it (either like this as a range extender or as a hydrogen version).
What I don't like is that they get the whole story of the 787B wrong already in that first paragraph. The Wankel wasn't outlawed because Mazda won with it, the whole reglement was known to change (to that 3.5 F1 formula) for years already. Mazda just set everything on one card and won that last year on the old reglement. A Wankel enthusiast should know that. And FIA "banned" it rather for the complicated equalisation with piston engine than superiority.
And don't expect the car to sound like the 787B, its engine will run at constant speed like in a generator (500+bhp still seems like a lot
)