> How is this different from just loading your world in a server and having your friends join?

Because player location, inventory, actions, are all load on the server. That's why servers have player limits.

> BitTorrent isn't going to work.

You and I are talking about different things. I'm talking about serving up the raw blocks alone.

And yes, I know, Minecraft servers don't support static file serving, or streaming from another source, or copy-on-write. I'm saying these are all nearly trivial to implement.