I.e. the FPS players could embody the military forces in a complex society where more RPG players are doing the diplomacy and strategy, others are playing in engaging "home front" social environments, someone is off doing city-planner/factory logistics stuff, etc. There could be some deep-diving, dungeon-crawling sub-games within all these realms, but also more casual modes too.

But, crucially, it is all tied together in a unified simulation so that these different player groups are actually steering a coherent story and state space for the shared world. The outcomes of diplomacy, warfare, industry, trade, local social groups, etc. should all have impact on each other.