I recently open sourced the worktree wrapper we use at my workplace, which uses reflinking in this way.

https://github.com/Applied-Intuition-Open-Source/stol

You could try proposing a worktree copy command on the mailing list. Worktrees are currently independent and work off of repositories which may have no existing worktree / working copy at all, let alone one it makes sense to start from, so there is bothing to copy but for dodgy heuristics.