If you "stack" your changes across multiple inter-dependent branches it looks like "git rebase" is going to learn how to update related branches using a new "update-ref" command (alongside "squash", "fixup", "exec", etc) that gets activated automatically through a "git rebase --update-refs" command-line flag and config option.
(This is from Derrick, not me)
""" This is a feature I've wanted for quite a while. When working on the sparse index topic, I created a long RFC that actually broke into three topics for full review upstream. These topics were sequential, so any feedback on an earlier one required updates to the later ones. I would work on the full feature and use interactive rebase to update the full list of commits. However, I would need to update the branches pointing to those sub-topics.
This series adds a new --update-refs option to 'git rebase' (along with a rebase.updateRefs config option) that adds 'git update-ref' commands into the TODO list. This is powered by the commit decoration machinery.
"""
This is under active development (I don't believe the topic has been merged yet) so it's still open for feedback and refinement on the git development mailing list. Thanks Derrick!
[1] https://public-inbox.org/git/pull.1247.git.1654263472.gitgit...