How many people are working on this in your couple years example? Is that just one guy or a team of 20 or something else? Whats the average salary for the team *n this scenario?
The deliverable would be a (theoretically) complete specification PDF like RISC-V's.
I have little doubt that I or Adrian could do it, or plenty of others. It might not reach the quality of something like AArch64 with that level of resources, but it's not hard to beat RISC-V.
I'd guess low six figures for the beginning of that list and mid eight figures for the end. Real silicon also needs all the uncore stuff, which is easy if you don't care how it performs and very very hard if you do.