Looks enough complicate to propose a patch. Maybe main contributor can follow without problem and know when theirs patches will be released but to external contributor, it's more complicate. We can't know if patch will be accept in next release, or in other next release, or maybe on step over (beta, backport, ...) .
In this case it seems easier to have personnal featured branch and rebase it when stable branch is released and don't propose PR. In this case, patches on stable release can be obtain but it's lost to the community, it's bad :/
I don't know how to do, but looks difficult to try to contribute.
Km