I might be wrong here, but don't Hyundai want to use hydrogen fuelcell powered electric cars, rather than ICE like Toyota?

But for real, WRC need to loosen up to rules a bit. They could get inspiraction from LMDh, where anyone can build their car on one of four different spec chassis from four different manufacturers (and none of them is big auto brand). WRC is killing itself by letting only big auto makers build and homologate a rally car.