Around the time I joined Tailscale, actually just before, I had a look at rsh with an eye in this direction. The problem is that rsh is very stale and unmainta

Around the time I joined Tailscale, actually just before, I had a look at rsh with an eye in this direction. The problem is that rsh is very stale and unmaintained - even those versions that have had releases in recent years (e.g. GNU Inetutils) are very old inside - even if they've kept up with patches, they have not kept up with features e.g. modern user session construction. It also turns out that ssh the client, much more so than ssh the protocol, is really a key integration point and API that users end up needing. It has a broad feature set that turns up in use cases all over, many of which rsh does not handle.