Don't Starve Together scratches the MMO itch for me. It's not an MMO, but there are public servers where you can hop in and hang out, raid bosses and whatnot. I have ~4k hours in it now.
Valve does seem to contribute substantially to the development of their games, at least. Turtle Rock's Evolve and Back 4 Blood had nowhere near the success of L4D/2, which is still going strong 15 years later.