UBlueOS as well as the increasingly popular gaming-focused Bazzite flavor hereof are build around the concept of an immutable kernel. This means nothing can write to kernel-space, and even with superuser privileges, you cannot do this. Updates are done by retrieving full & tested images, you can always roll back to the previous image, and the system doesn't really complain if it runs out of storage. I believe that some of these features are in line with Protons mission for helping users achieve security and privacy. Achieving support for the immutable Fedora-based distributions would mean extending support for the rpm-ostree package manager, which creates layers on top of the immutable image. These layers can hold rpm packages, and therefor fits well to your support for Fedora. Support could also mean opening Proton support to a limited but still available support for these distributions. It would be amazing to be met with just an attempt to help solving issues with f.x. the CLI install on Bazzite.
I hope you will consider this.