I could be very wrong, but it's not about being a niche or not, I think that other than the "sound" there will not be the cultural background for shaping the rally as it is now and as it has been the decades before.
There is no more symbol of the car as the freedom of the individual, the car will not represent anymore your status in the society, there will not be the masculine culture around it. Sounds and performance of actual engine fits perfect with that rapresentations, electric cars and automatic cars don't. This is why in my opinion there will be some huge change.

(Regarding rally as the second motorsport, they were referring to the car motorsports and not in general, so motogp is not taken into consideration. It sounded a little weird to me that Nascar and all those american things were behind WRC in terms of popularity but maybe they are more confined into US borders than WRC into European/Oceania).