According to Adobe they are completely reworking the rendering engine to make it more efficient and to take advantage of more system resources. The old system was not very efficient so I don't expect you'll see the same option but instead you'll see all cores being utilized and maybe even the GPU to render more efficiently. Asking to return to render multiple frames simultaneously is kind of asking us to all go back to a horse and buggy when you understand how primitive and inefficient the old system was.
Yes, but it would be helpful to at least know about an approximate implementation date.
The new features work really well but without the horsepower to get everything rendered in time doesn't do any justice.
Adobe is always working on improving their products. This is high on the priority list. Not even the team knows when things will be ready for prime time but I expect performance enhancements are high on the list for the next release.