I can see close to zero possibility that the majority of the work will be shifted to the CPU. Anything a CPU can do can just be done better with specialised GPU hardware.
Nope. Anything inheriantly serial is better off on the CPU due to caching and it's architecture.
Many things that are highly parallizable are getting GPU enabled. Games and ML are GPU by default, but many things are migrating to CUDA.
You need both for cheap, high performance computing. They are different workloads.