The problem with waiting for the patents to expire is you're always stuck 20 years behind.
Being 20 years behind isn't a particularly big deal if those 20 years are basically just SSE3, SSE4, AVX.
https://fuse.wikichip.org/news/3099/centaur-unveils-its-new-...
IIRC you watch the "Rise of the Centaur" documentary they talk about the Intel lawsuit, and the corresponding counter suit that they won. Which makes the whole thing sound like MAD.
More interesting there is https://en.wikichip.org/wiki/zhaoxin/kaixian
In some ways, it actually frees them up a bit; as they don't have to reciprocate any efforts with Intel. Which they tried to leverage with their Padlock technology. Unfortunately, their marketshare limits any real practical usage of those benefits.
Uuuuh, presumably the case was about patents, right? I don't see how cleanroom-ing is fine with regard to patents.
Oddly enough, integrated circuits have their own IP scheme. IP has copyright, patent right, trade secrets, trademarks, and mask works. You rarely learn about mask works, since they're so narrow.
https://en.wikipedia.org/wiki/Integrated_circuit_layout_desi...
I think a lot of this would hinge on that corner of the law.
Summary: Cyrix (and subsequently, VIA) have an implied license to Intel's patents; allowing them to develop x86 hardware.
How that differs from AMD: AMD and Intel have a full cross-license on technologies. This means, AMD can utilize Intel resources to integrate AVX-512, a ring-bus, etc (and vice versa). VIA can not. They must develop those technologies independently, in a compatible manner.