ARM or something like it will move into PCs. It is inevitable. You can only miniaturize components of an ATX form factor machine so far before it becomes pointless. And without relentless miniaturization, the computer industry will die. CPU, GPU and BIOS will merge. Eventually RAM and solid state hard drives will be incorporated too.
No it won’t. There’s no need for miniaturization in PCs, they’re 99% air. Even in laptops owing to the necessity of usable keyboards and readable screen they don’t need to get much smaller than they already have. Portable stuff needs things to shrink, non-portable or semi-portable has already hit the size it needs.
GPU only to an extent (lower end users). Mid to Higher end systems will still rely on GPU’s that have the power and flexibility for demanding jobs and even games.