I think similar ideas have been tossed around. The big difference, I think, is that the entire server would be able to build and play at the same time. Previous suggestions were having a small group build it, which was untenable, given the enormity of such a project. This is why I focus on smaller games in Frog Park, because they can be finished without consuming all of our minecraft time. World building is one of the most time consuming activities, and least efficient in terms of time-to-gameplay. If I can create a game in a 32×32 area that’s just as fun as a game in a 1000×1000 area, guess which one I’ll build?
Another similar suggestion is using something like MCMMO, a plugin designed to make it more like an RPG. But if you look at it, it does a lot of silly things. Like, if you punch ~5-10 mobs to death, you level up your punching, and suddenly your punching strength is greater than a weapon. What benefit does this have? None that I can see. It’s funny to 1-2 hit mobs with your fist, but it doesn’t make things more interesting. Perhaps it gives a more guided experience, which some players need in open worlds.
I’ve been contemplating the idea of inserting NPCs into our main worlds. So that people can liven up their existing builds. One thing NPCs can do is give quests. Although, I’m not sure quests are inherently more fun. Plus you can already do this with shops or player requests. (quests are just simulated demand) There’s already plenty to do in the game.
Bosses could be a thing. Mobs with greater difficulty to kill and higher rewards. However, this is hard to do. Anyone who participated in Easter could see the potential in this, but there’s only so many rewards that would be worth the risk.
It’d be interesting to experiment with this on a smaller scale. I’ve always wanted to setup our intro area as a mini-RPG/adventure.