I've been working on a multiplayer rpg using colyseus. You can find it at https://rair.land. It's pretty old-style, and it currently looks like this:

I make use of colyseus by making each room correspond to a map in the world. That way, empty maps aren't loaded or taking any resources. Rooms with fewer players will still take fewer resources than a normal, populated one, since anything not near a player slows down significantly. The loot on the ground is persistent, same with boss timers, so you can't cheat the system.