Yeah, PCSS implementation is still experimental in UE4, so I think improvements will be implemented at some point.
I haven’t looked in-depth at PCSS in UE4, but I can tell you that in regards to shadow filtering, you always have to choose between either banding artifacts or noise, depending on the sampling pattern.
The biggest problem for you right now, is that noise changes each frame, even when the camera is stationary. If you ask me, I think that it is only acceptable, when camera is in motion.
Usually penumbra sizes are quite small and temporal aa does amazing job at getting rid of the noise, but in your case, perhaps, modifying PCSS code, to use a different sampling pattern is what you need to make the noise less apparent and frame to frame coherent.
Going from sobol random to a much simpler fixed disc is probably worth trying.