This has always been a thought of mine. I wanted to replace/remove any non-free kernels with a libre kernel that doesn’t provide non-free binaries. I know some people say it does not matter, but I think it would be a cool idea.
I was thinking about hardening QubesOS by possibly using a deblobbed version of the Kicksecure kernel on all VMs. It would also come with Javascript disabled entirely on all VMs, all non-free binaries removed, everything run over Tor by default, maybe creating a custom repo with only free software, etc.
This would be inclined towards people who use Libreboot/Canoeboot, specifically those that use systems like OptiPlex 9020 and T440p, that run only 100% free software in the BIOS.
I’ve never attempted it, but I would like to know if anyone would be interested.
It should be pointed out: deblobbing a kernel does not necessarily harden it. Secure and libre are orthogonal concepts. That being said, I like your idea.