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You're missing the point! After FIA opening homologation to private tuners the interest over GT class increase hugely, and that could also be the case with R5 (nowadays limited to 3/4 manus) and even on the other R categories (there are little more than 20 models homologated, all classes combined).
Rally fans needs diversity of models on stages and drivers could be able to choose their cars from different tuners, instead of having to pay a fortune to the established ones that profit from FIA strict homologation methods.
In Gr.N/A days there was an enormous variety of models homologated from almost every make and a huge number of capable private tuners, that could provide competitive cars at a fraction of the cost of a works car.
With the exception of WRC cars, the pinnacle category of the sport, R classes homologation process shouldn't be so oriented to manufacturers, and FIA could easily replicate the overture to private tuners like in R-GT.