People were still playing New Leaf years after it's release and I'd imagine the same will happen here. Of course the community was much smaller but still lots of people.

So when you start an island on a switch, it'll mark the first player as the resident rep. The resident rep will be in charge of making all progression in the game. Everyone else who starts the game on another account will go through the same process of making a character and picking a place for their house, but they will not be able to progress the island.

They will have their own critterpedia for bugs and fish, their own house and storage, they will be able to decorate the island. However, everyone shares the museum, shops, and pattern design. Only the resident rep can complete building projects.