It's like a crossover episode with SpecialStage in here.
There's been plenty of talk about tuning to run on E85 and that would be an interesting option for a sub category or class. For the horde of WRXs out there it would be a matter of tuning and maybe a few bits that wouldn't be too expensive compared to the rest of preparation, especially if it could be offset by the availability of E85 in bulk at rallies.
Diesels would be interesting, too, but there just aren't enough available in the US right now.