Although the possibilities are arguably greater for new designs to get traction today.

There are a lot of reasons. Open source, cloud providers, etc. But a big one is that you can't just depend on CMOS process shrinks to make processors faster. Therefore, your new design isn't necessarily going to be eclipsed by whatever new x86 CPU comes out in 12 months.

That's true, but the difficulty is it's not just going to take 12 months to do something like this. A radically new architecture would take years to become competitive with today's processors for all of the use cases that would make it marketable. Meanwhile the x86 guys aren't just going to sit still, there's almost certainly more IPC to squeeze and they can add fixed function hardware (as they've already done for video encoding/decoding) or FPGA area in new product ranges and keep building new markets that way.

I wonder if something new could emerge to help with massive parallelism, beyond what gpus already do.

An instruction to insert into a queue on another core would be a great thing. The T3E had it, InfiniPath / OmniPath has it between boxes, and I've heard of a research project that did it on a modern cpu.