Unfortunately, going from there to an affordable chip with reasonable performance doesn't seem possible.
You can certainly get Power cores with the VHDL and everything; the most notable of these is Microwatt, and IBM even maintains it. There are also A2O and A2I.
That said, I don't think it's reasonable to expect that a company that put R&D money into designing a high performance chip should give away the store. There has to be some incentive. I'm satisfied that I don't have any unexplained or opaque firmware blobs in my POWER9 chips and the ISA and its internal workings are well-documented. That was good enough for the FSF, and it's good enough for me.
There is a deskside POWER10 machine from IBM, that uses their smaller half-rack server, but it has somewhat limited expansion capabilities.