For there is no possibility to displace Materials in RPR at the moment, i just found some node setups for rudimentary parallax mapping for eevee/cycles on Gumroad and Blenderartists:
Because of many different nodes it is not working on RPR right now, and, as i said, it's very rudimentary.
I asked myself, if it would be possible to interate Parallax Mapping in RPR? It looks so great in UE4 for example, and it's that fast compared to real displacement (which, no doubt, is unbeatable for very close objects)
I think it would be a great chance to speed up renders, while keeping a lot of detail depth.