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SWG Pre CU did, infact they were called Themeparks and they acted out as little quest hubs you did for a badge mainly. It's a bit like the real world where you have your sandbox, can do whatever you like in it and then you go to a Themepark for some fun. The only reason why people overlook this is because the content in SWG was poorly made, rushed and wasn't fun. It did have the right ideas however, sadly they get overlooked and because these themeparks were dotted all around the world with no levels you could do them at any time. This would always end up with new and old players doing this content at the same time because it's when they chose to do it and not when their level did through a linear world.
Themepark MMOs become top heavy and dead, this is why the solo MMO has come about to try and fix this. Why hasn't the genre gone in the logical direction of non linear content? It seems like a much better fix where no parts of the world die and you can always get a group. There is one MMO that still exists like this today and it's called EVE Online and every part of it's world is still populated. SWTOR could even learn a bit from freedom, instead of making them horrible Fleet Stations which turned the game into PSO, they coulda let the community decide on their hub like how Jita is in EVE.
People always look at old sandbox games and think "it means no content" and I think the reason they had no content is because not even themepark MMOs did back before WoW when these sandbox games came out. WoW was really the first MMO to come out where you levelled from 1 - 60 on quests alone. It also set the bar on what people thought of as a dungeon from The Dead Mines. Usually at level 20 you'd get a room with 3 mobs standing in it at that time, then WoW gave you like an end level experience at 20 lol.
I'd really love for developers to realise an MMO is a virtual world and to make one, instead of a linear level. You can make a non linear world with linear story experiences in them as the shape pf themeparks. The real world is like that and it works, so it'll work in games too...