Prevents people from joining in world UNLESS you give permission to, GMS wont let people warp, world wont show in active worlds and to join you need to type the name manually. However, mods might have like a item that shows worlds like this, but inside the worlds, you cannot drop items. This would be good for people who don’t like being bothered while farming etc.
Interesting idea it isn’t exactly needed and if you want at the entrance of your world you can create a fan vortex thing which does the exact same thing it sounds like somebody would find a way to use it to break the rules
But overall not really a bad idea