Exactly what glitch is fixed here? Is there a problem with highlighting to a customer that the battery may not be authentic? They aren't preventing you from installing aftermarket batteries at all... This works just as well on a 6s as it does on the brand new ones.

The "glitch" was users replacing batteries without giving Apple a revenue stream.

You are correct that it's still technically possible to replace a battery yourself, if you don't mind the Shareware-style nagging.

Shareware-style nagging? You get the pop-up when you boot the phone... then you can just dismiss it. What are you talking about? The notification in the Settings forever seems fully appropriate, since that is something I would want to know if I was buying a phone from someone.