how about a game like anno1777 ?
it looks sustainable, players get real money in and out,
I can't quite get the busyness model, but players are happy
Wow, anno1777 sounds intriguing from the feature list. However, the site shows nothing of the game itself. From the description, it sounds like if that's what you want, just play anno1777! Sounds very hard-core though, in terms of the environment. My idea is rather more light.
I am playing it, and it is not so heavy as it might seem,
player only has his 1 page with 20 buttons,
"buy food", "go to work", "rent a house", "attack" and status is printed in text,
there is no graphics at all, only a few places where timer is running
there is probably a lot of work on database in the background,
in coordination of all different aspects of the game.
if they only accepted bitcoin...
one nice idea from anno is that they pay dividend to shareholders of the game,
shares and dividends are handled directly within the game, player has a button to buy or sell shares at all times
dividends are paid after game fund reaches 10k eur, it happens at least once a month, and dividends pay 1 cent per share,
one share is 32 cents, so it is quite impressive,
it has been going on for a few years now, and seems sustainable