> Couldn't there be some way to just tag the "main" commits and mark the dead ends as "extraneous" rather than destroying them? And then have your history-viewing tool hide/squash the unmarked "invisible" commits by default and only expose them when specifically requested?
You could do exactly that; look into git-update-ref for how you could implement that so that garbage collection doesn't wipe out those dead ends (git-notes basically does what you would need to do).
Note that you would still be rewriting history, still rearranging the DAG, but you would have references to the old states. Basically like a permanent reflog, though perhaps with an interface tailored to this usage.