[throwawayish]

> the lot of them are closed source

That's wrong. See OpenSPARC, where you can get the Verilog code for the T1 and T2 (Niagara-based) processors. (IIRC this was only one year after their commercial release).

SPARC in general is perhaps not a bad example, since the ISA is open and royalty-free and there are actually independent implementations (well, today only Fujitsu and ofc. Oracle).

It's quite interesting to see RISC raising again after it died rather harshly in the late 90s -- were literally every year a major manufacturer announced the end of an architecture -- and early 2000s (and remained dead rather firmly throughout the 2000s).