That sounds like a nice improvement, just like many other aspects of jj!
Tools should adapt to us and not the other way around, but if you are stuck with git, there's a slightly different workflow that supports your use case: detached head. Whenever I check out branches that I don't intend on committing to directly, I checkout e.g. origin/main. This can be checked out in many worktrees. I actually find it more ergonomic and did this before using worktrees: there are no extra steps in keeping a local main pointer up to date.
The detached head is what I meant with keeping it on the branch while not keeping it on the branch.
The complication comes from trying to stay current. With a regular worktree I could just pull, but now I have to remember the branch, fetch all and reset hard to the remembered branch.
Tools should adapt to us and not the other way around, but if you are stuck with git, there's a slightly different workflow that supports your use case: detached head. Whenever I check out branches that I don't intend on committing to directly, I checkout e.g. origin/main. This can be checked out in many worktrees. I actually find it more ergonomic and did this before using worktrees: there are no extra steps in keeping a local main pointer up to date.