Low level changes in the kernel will probably take a long time and effort before they are deployed. Many kernel devs probably don't do their work because they need some particular fix for themselves, but rather to advance the overall product.

I'm not trying downplay the most amazing community effort humanity has ever seen. I'm just saying, if you want even a basic CPU, it will take far more generosity than that of a few humans to get it off the ground. Insanely more to fix one, if it's even possible, let alone practical.

The initial versions of Linux weren't useful except for people playing around with it -- kind of like RISC-V cpus aren't useful today, except people playing around with fpgas. But it does allow you to relatively easily deploy your CPU using this route.

I'm saying that much linux development nowadays is done far away from actual deployment, just like open source cpu design would be.

Also, it's often paid and driven by companies who have an interest in the existence in these open platforms, so it's not all just based on generosity (and we do see companies are interested in RISC-V cpus).