Perhaps We're not on the same page here... if we are talking WRC Spec cars (Those that are run by Manufacturer teams in the WRC) they are NOT required to have roadgoing counterparts. Total output for WRC Homologation is less than 50 cars.
You may be thinking of the older Group A vehicles. Prior to '97 I believe these (and the now dead Group B cars) were the frontrunners in the WRC. They require a 2500 production run. You may also be thinking of Group N cars which require a 5000 car production run.
I don't believe there are many of these vehicles(aka "Homologation Specials") being made currently.
Regardless the WRC specifications DO NOT require the base car to be AWD or 4WD. Manufacturers are allowed modified 4x4 transmissions regardless of the production car's transmission.
The reason I doubt the MSP would be used is because its is basically a factory tuned Protege. Since it is tuned for performance street use I don't see any reason that Mazda would bother with using it for a base car when they can take a step back and use the protege/3 instead.
Ignoring all of which, the MSP was a limited production run car. It would not be a good idea to base a vehicle that is updated & re- Homologated every year on a car that will not be around come next season.
on rotary engines - I don't think there's anything that says it has to be a piston engine, but there are limits on displacement and turbo size and I beleive on HP as well.
I would be far from oposed to seeing one in a rally car someday
