Earlier quoted context omitted.
> tui-based MMO As in, a MUD [1]? There are still a few around. [1] https://en.wikipedia.org/wiki/MUD
A MUD is a text adventure - as in, requires lines of prose commands. I believe a TUI MMO, in this sense, would be closer to a Roguelike or an action RPG, since it can process key presses directly without linebreaks.
Few months back, there was a story here at HN about someone writing just such game to be played over a SSH connection. There were huge problems with the fact that you cannot reliably detect when the user stops pressing a key.
IIRC, it was an action/arcade game, though, so it might be more tolerable for something not twitch-based.