Right, so imagine a fairly capable VR. You can visualize anything, it can tweak the VR to make it seem like you have various amazing levels of skill at whatever, etc. This is an RPG, but it would be useless to compare its 'rules system' to anything like D&D... It might be literally built around D&D tropes, so there are beholders, mind flayers, red dragons, Demogorgon, whatever, and some version of D&D cosmology. It might even be set in some D&D IP like Faerun or DS, but play would be a lot more like LARPing than existing TT RPG play.
The main thing that will be required is a LOT of AI and support systems such that GMs can translate their ideas into visualization at a sufficiently detailed and varied level, and that things like NPCs/Monsters will play in an acceptably sophisticated manner. Some of that is in reach now, video games have generative detail and enough 'AI' to be challenging combat opponents within narrow parameters, but decent depth in social interactions and linking that together with plot elements and such is nascent at best (modern games are, in this area, totally scripted). So it is hard to say how close all that will be in 20 years. We might blow past it, or we may still be trying to figure it out.