I would never run a mush because I lack the skills to be staff let alone run a game! But if I did make a mush it would be...
An original fantasy Lord and Ladies style game in which a large Kingdom has been pushed back by an evil blight onto a smaller and smaller area of land over time and no longer has the resources needed to maintain their population and must find a way to reclaim some of their own lands fallen to darkness once again if they have hope of providing for everyone eventually.
So a large group was gathered up to travel into the blighted lands and to try and bring it back. Some where volunteers who did such out of honor, some joined for money, some to pay off debt, some to feed a family the left behind and etc. Some are nobles some are commoners. Some are fighters, rangers, healers, mystics, survivalists, hunters, priests , weapon smiths, armorers and etc. But everyone has a skill that might be useful while on a survivalist mission fighting the darkness.
And the game takes the group (all the pcs) as they travel through the blight, make camps, fight over the course of years trying to restore the land for their kingdom. New people can come from the Kingdom and volunteer later (allowing new characters to join up later) and sometimes the party might return the Kingdom at times. People can leave (stop playing) and leave the adventuring group for the kingdom.
Lots of characters die fighting. Battles, ranging scenes are pretty regular and prps are encouraged.
People can go on side missions away from the main group. Sometimes they camp in one area for extended period of time, but no perm homes are made at the start anyways.
The Grid would be each character having a a camping tent, a group camp/fort (multi rooms) and various sides rooms for adventures and prps.
Characters can get married while on the adventure, but they all know they might die and marriage and children is not typically their goal of those who volunteered. That is for nobles who stayed at home.
Eventually as the story progresses some areas they reclaimed might be settled and built up and the grid expanded and some characters might stay behind in those places if they wish, turning into more of a settled Lords and Ladies game. But the blight must be always be watched for and fought back against.
This came would basically have lots of battles with blight trolls and lots of survivalist type scenes, tracking, hunting, finding edible plants and etc.
The everyone having a tent build would allow people to have a place for private scenes even on a game that is focused on the game being largely together while on a mission. And the side missions, scouting, skirmishes etc allow people do prps that don't involve /everyone/.
The volunteers who stop fighting for a while and return to the kingdom or volunteer after the mission started and join later allow people to come and go from the game as needed.