I did exactly this and use it as a "file system adapter" on my WordPress installation (to handle uploads/media). I tried to submit it as a plugin but they said "no" because I can't use "git" in the name -- and fuck that. So, I'm the only person on earth that does this (AFAIK).
Do you have this plugin available anywhere at all? I can't say it'd fit my workflow or anything without knowing more (so don't go out of your way!) but I'm very intrigued in to how it works
No, because a branch is a (re-assignable) name for some commit and cannot point at different commits while in the same repository at the same time. A "branch but at different commits" simply makes no sense. You can however create a worktree with a detached HEAD pointing at any commit. By default it seems to create a branch for each worktree.
You can have multiple work trees for the same commit, for that matter, as long as they are the same branch (so with different branches pointing at the same commit, or detached heads)