Well, this is a decent start:

    $ git remote add newbloghost http://somethingnotgithub.com/example/path.to.git
    $ git push --set-upstream newbloghost gh-pages

I think you are missing the point of git.

I think parent meant github.

How decentralized are we talking? Because there are more shared hosting providers, VPS providers, and domain registrars than I can shake a stick at.

If you don't want to depend on GitHub, there's nothing stopping you. I host my site on a VPS and couldn't be happier.

Jekyll is open source and it can be run on any server (I always use it locally) and its output is just static HTML, which means it can be served from anywhere.

You might want to check out using CI to build your site. It's really satisfying to watch the commit -> push -> build -> deploy cycle.