Objection! Hehe... No, wait. Really, I see a problem...
If registration are closed, mods would be exclusively from outside. And, since reports are not federated, this communities would be prone to difficulties for moderation. Unless reports are correctly federated, I don't think this is a good idea. And, even if you were to open registrations only for mods, we would have only moved the inconvenience to this (who wants to have so many accounts, really?)
There's also the problem with centralization of domain names under you. I don't know you, and perhaps you're well intended.. So, it's fine for the most part, let's just assume that's okay. Now, what happens if you had an accident or decided to go live in a farm? Without domain name renewals, etc. all communities would be in trouble. There's centralization in the shape of a single point of failure.
I can't see this happening even if the domain names are cool.
And, leaving disadvantages aside. What's the point on this? Can you name any advantage?? I agree that it would be more ordered and I like that. But it's quite subjective, and hardly anything huge to really break the inertia or status quo of things as they're now...
Thanks for the intentions. Let's focus on some new ideas, they'll come...