Not a Mesa maintainer, but I've been following Mesa upstream (and in Debian) for quite a while.
If someone is going to backport Mesa, just going to note:
1. The firmware-nonfree source package will need to be backported for hardware like newer AMD graphics cards to work with the later versions of Mesa. Currently this package isn't in stable backports, even though the newer kernel is.
2. While Mesa 22.2.* currently only needs llvm 11 (based on the meson build file), future versions will need llvm 13 or later (for building newer Intel CLC support). This means the llvm-defaults source package will need to be backported as well so that later versions of Mesa can be brought to backports. Should not be an issue "right now", but definitely adds another thing that will need to be backported ongoing.
3. There is also the question on whether or not to also backport Mesa Amber (aka Mesa's legacy driver release) in the future. I don't believe that has made it into Debian even yet (tho there's been at least one attempt that I saw on the Debian Mesa maintainers list).
None of these should be show-stoppers, and #1 and #2 have been done in the past for backports of Mesa.
BTW: Would love to see mesa backported. Knowing what needs to happen is always a good first step, and also may help others understand why it might take a while.