There is no reason a TUI couldn't do this. Calling another program is easier in a TUI, since it is one step nearer to execve and a shell. If it is in a file, then opening another program isn't hard.

> The TUI I'm working with runs on a pair of Linux VMs, and is accessed from Windows, Linux and Mac, so asking all our users to enable X forwarding doesn't really work.

Run another Linux VM on the client. /s

Aren't there X servers for Windows? I remembered installing one on a locked down university computer for fun.