In a sense it's already happened, all it takes is an RPG that gains enough mainstream awareness to pull new players directly rather than sell itself to market already selected for at least being able to stand D&D.
Each time it's happened, we've narrowed our definition of RPG to exclude the interloper, spawning a 'new hobby.'
CRPGs
LARPs
MMORPGs
Did LARPs ever get heavy adoption?