A global chat and individual rooms limited to x people (Four in that image?) is not what most people think of as an MMO. And in the case of a card game you could probably even go the hackey route of just implementing a layer over IRC to accomplish what you’re after. That way the server has to process chat messages, and game logic for only those who are playing. You’d still have some optimizations to do on the card game simulation, but you’re right: it’s absolutely within reach even for indies, especially if you go the hackey route. Also worth mentioning that in that case the number of spectators is irrelevant.
But we both know that’s really not what most people are talking about when they want to make an MMO.