There are several points.
The first thing is that Rally2 simply don't make sense as a marketing tool for the manufacturers. Simply said they are an advert for times that passed. The marketing departments of the manufacturers won't ever permit massive investment into promoting petrol cars.
Second thing is that the true manufacturers don't want that. Why? Because the last thing their public image needs is some privateers beating them.
Third thing is that now the Rally2 cars are quite equal and affordable cars. Once the works teams start to use them as the top class the equality is gone. In one or two years maximum the cars won't be equal anymore. And not only one type to another but also cars from works teams compared to the cars from private ones. The real running cost of a competitive car will rise immediately as well no matter how strict the rules are.
The first point is the most important. WRC must decide whether it will stay as a top tier championship where massive money of the global enterprises are being spent or a sport of hobby drivers. In first case WRC absolutely needs to find a story to promote in the future. That is missing now. Everyone and his dog can see that WRC fails to find a viable concept for its future. Today the WRC only lives from its past and making Rally2 the top class would just underline that.
The other option is to fuck the enterprises and make WRC a sport of private hobby drivers. In that case you have to prepare for money leaving the sport. It means that in a few years live coverage will disappear. Some iconic events will start to disappear because the government support will disappear. The TV coverage will start to disappear etc.