Sure, a new processor that is designed to be optimized for a different threading and memory model might be better in a lot of ways, but backwards compatibility

Sure, a new processor that is designed to be optimized for a different threading and memory model might be better in a lot of ways, but backwards compatibility is important. We can't simply throw away all of the existing software written in C, and in most cases a regression in performance for C programs would be unacceptable. Sure, such a processor might find niche use cases, where it doesn't need to run any legacy software (including OS) and can take advantage of massive parellism, but I don't see it being able to replace the prevalent abstract computer model used in CPU's today.