And all major chat rooms are hosted there too. That's not how matrix works. Rooms are fully replicated to all participating servers, no single server acts as a point of failure. It also has a resolution system for divergent states; no server has authority over any other. You can add local aliases for any room you're in on your local server without permission from room admins. (... Actually I'd have to doublecheck that. It might be one of the permissions.) You don't even need an alias, the room ID (eg. !BZVTUuEiNmRcbFeLeI:matrix.org) and a server that's currently participating in the room (ie. has that room ID) is enough to join. That's really what aliases are; mapping a name to a room ID on a particular server that is known to be participating. Room IDs include a server name as an anti-collision mechanism, it has no other significance.

It feels like 95% or more are on matrix.org instance. I think it's a bit lower than that. midov is actually pretty big. So's T-AC. (And then there's joe's room directory, which I think is bigger than morg's.) But it's well over 50%, which is disgustingly high. morg should close registrations, and purge dormant accounts/aliases.

a weekly cap for new registrations as an option Extremely good idea.

like MMOs. Funny you mention that, I had a laugh on Witch Weapon when I discovered that my server was frequently getting 10-100x more points in ranking events than other servers (and I was frequently placing top 50 without any of the busted characters). I'd simply chosen the recommended server, which I had assumed was the smallest at the time. Turns out it was just a static value so it had like 50x the population of the other two.

I still miss that game.