This is a very informative and well-written article. One thing that would make it even more useful to me would be links to (the MediaWiki pages of) extensions that implement these different ways to register services.
An example of "includes/ServiceWiring.php" can be found in the CirrusSearch extension.
An example of registering a custom service using the MediaWikiServices hook can be found in the Global Preferences extension. See "extension.json" and "includes/Hooks.php".