I know this is a bit forward, but after watching the video on what they have already with the biome generating. I think with the lore they should eventually expand the world to different planets like the system they have going now. These different planets should be vastly different and have some that are habitable and some that are non-inhabitable.
This may equate to the same function as moving away from home and the mass of other players and allow people to stake out places in the world. The other function I could see this having is setting up biomes and different worlds that have increasing difficulty and are much harder to go to.
The awe from first arriving on a world where danger is everywhere would make people want to get to the point where they could go there and see what is available. I think some procedural generated worlds with extremely expansive dungeons and depth to them would allow people to explore forever.
Thinking ready player one esque where it would take multiple years for even one of the biomes / planets / areas to be fully cleared would have people that would be needed for building and gathering resources to throw at it. The naturally skilled and tactical to tackle the location and the extremely dedicated to get the the end of one the zones.
Of course having different rewards along the way would allow people to get into the action without having to go full in but giving people the unlimited expanse to just dive as deep as the ocean can take them would bring a truly amazing experience!
edit: I also wanted to note that sword art online the anime does this quite well too where there is just an expanse of time that it takes its players to reach the end of the world, this would allow people that want to invest to do so. It makes those jobs that are sorta capped to have meaning as they would need endless supply to pour into the people taking the leap into the unknown.
Don't be afraid to bring difficulty, this is both the age of information where boss kills spread like wild fire and people will ban together in forums and in game to challenge anything you throw at them. I bet that the difficulty will draw crowds and including people that have craved this adventure for years.