John Bridgman of AMD confirmed it's their plan like 5+ years ago. The only reason they ever maintained proprietary stack on Linux is workstation users who need certified OpenGL implementation for various proprietary software.
By now the only proprietary parts of "pro" stack are OpenGL implementation and shader compiler for Vulkan / OpenCL. Everything else in "pro" package is open source already. There is still legacy OpenCL implementation, but I guess ROCm will be used for everything soon.
Now, with NVidia diving more and more into the ML / GPGPU market (which is less windows-focused), they might have more pressure to actually open-source their driver (or at least, finally make them actually integrated properly with Linux), at least for their server focused hardware. But I wouldn't bet on it any time soon.
Let's be honest, they have a dominant position on the market. And their driver, as awful as they are, work. I think a lot of things would have to change for them to have the incentive to open-source them. My only hope at this point is that, with the growing GPGPU market, they might finally start to see Linux not as a second-class citizen.
Interestingly, amdgpu/Mesa performance seems to be higher for typical game rendering than AMD's proprietary stack. I suspect at some point in the future AMD will abandon their 'pro' proprietary stack entirely after realizing they should stick to being a hardware business.