Maybe. There's a lot of other things to do before that.
Watch this https://www.youtube.com/watch?v=fsMTXgqdYxg They kind of answer the question mentioned above. The, "Holy Grail is GPU & CPU." The real question is Does RedShift, VRay or RenderMan, have the "Holy Grail"?
Redshift doesn't. Yes you can enable cpu and gpu but it slows everyting down. Clarisse and Karma (Houdini) are in beta. I think it's a really difficault process for devolpers
Did some tests with Vray 6 in Hybrid mode.
Its does use the CPU as a CUDA device. Its slower in our typical scenes than GPU only in RTX mode. But faster than GPU CUDA.
Arnold would be better served to just fix the problems they have. GPU rendering is unstable at best. It doesn't allow for any kind of transparent alpha and you have to jump through hoops to get it to 1. Render and 2. Look decent