New subcommand for git-annex remote

[Apparently, I can only put two links in this post. See GitHub issue #7625 for a fully-linkified version of this post.]

Hi folks, is there any interest in a new rclone subcommand that acts as a git-annex remote? The term "remote" is unfortunately overloaded by git-annex and rclone; I'm describing an rclone subcommand that speaks the git-annex external special remote protocol, enabling git-annex to store and retrieve content from rclone remotes.

A similar project called git-annex-remote-rclone already exists, but my primary complaint is that it does not support git-annex-export, aka "tree exports". As a result, the content exported from git-annex to an rclone remote is opaque to humans -- just a bunch of files with names like "GPGHMACSHA512--${DIGEST}", not a browseable file tree.

I think there's also some potential performance improvements if we move the client into rclone. For instance, it could support git-annex's ASYNC protocol extension rather than transferring files one at a time. I assume there's also some overhead to exec-ing rclone once per file that could be eliminated with a more persistent client.

This is admittedly pretty niche, but I'd be pleasantly surprised if there's any community interest!