The problem with Windows RT was the gimped API. If Microsoft had used that opportunity to completely do away with their "backwards compatibility is sacrosanct" ethos and exposed an equally capable API then app developers would have flocked to it.

I remember being at a product design meeting when Windows RT was about to be released and every feature that we wanted to bring over from our flagship x86 software, our tech lead kept repeatedly saying "no we can't do that. The API does not allow it". Finally we said fk it, let's come back to this in a year or two after Microsoft gets their act together. And we never did.