I don’t have a lot of experience with displacement maps but as far as I know you still need a very high res mesh for the map to work, right? While this is an alternative, it’s not the right one.
P.S. Yeah, I know this question has been asked a lot but if anyone has heard any rumors, it would still be something.
There is a way to subdivide the mesh in the renderer instead of using a modifier. And bumpmaps do not need subdivision. Before giving it up you may want to try and experiment.