And it’s really opaque. Would be fine if it were an open source package but there’s a lot of mystery behind how it’s implemented.

I don't find it that opaque. Even without trying to deobfuscate the obfuscated source code which Microsoft ships (I haven't tried but it wouldn't be hard) a lot of details about how it works become obvious just by reading its logs.

Of course, it is a pity Microsoft doesn't open source it. But there are some well-maintained open source alternatives, e.g. https://github.com/jeanp413/open-remote-ssh and https://github.com/F1yingWhite/fast-remote-ssh (I haven't got around to giving either of them a go–but I really should.)

Exactly! Like if I'm admining a server what am I supposed to do? Message on a big slack channel and have everyone ignore me? It's easy when people are just logging in through normal ssh as I can put a big bright warning message on their screen that they can't ignore.

Also, timeouts...

Also, does anyone know if VSCode supports mosh?

Could just put this in /etc/bashrc.

    if [[ $TERM_PROGRAM = vscode && -f /etc/motd ]]; then
      cat /etc/motd
    fi
Assuming your users use the integrated terminal regularly