I think Ubisoft's "The Division" meets and melds some of the concepts you're talking about in the direction MMO's seem to be going. You start out grabbing a few

I think Ubisoft's "The Division" meets and melds some of the concepts you're talking about in the direction MMO's seem to be going. You start out grabbing a few solo missions, and the game procedurally teaches you elements of the game by making you...well...go out there and kill bad guys. Periodically in early game you'll be on a mission, pinned down when a bullet whizzes by from out of nowhere, oh look another player walking by decided to come join. That's when you learn about forming parties. So on and so forth. It's not a perfect experience by any means (especially on PS4 which seems to both fall behind in updates and seem to be the buggiest port), and it does get a bit "grindy" at times, but for me it's been quite a unique experience. You can very well solo some of the missions, but you will be punished for it. My main critique is that end game (the "Dark Zone") is essentially one giant arena built for "let's see how far I can push the gear envelope today".