I do not know if this has been proposed already, but a quick find did not yield results I was looking.
I have thought that with the virtualization suport now available in many ARM SOCs it should be possible to build a minimal Linux-based "shim" distro with the patched kernel that would serve as a virtual environment to run distros that have unpatched kernel. The shim distro would provide the payload distro a standardized environment and paravirtualize things like GPU acceleration and network while being as transparent to the user as possible.
This would not be an ideal solution when compared to mainlining the support for all the ARM SOCs, but as the mainlining efforts seem to be quite slow, this would improve the user experience particularly what it comes to running less common operating systems and reduce the burden of the SBC manufacturers for what it comes to maintaining images and kernel repositories for different distros.
With things like virtio-gpu this should be possible, but $someone should put the existing pieces together in a nice package.