Suppose Apple standardizes jailbreaking: say they allow you to turn on a switch that creates a sandbox on your device for you to do whatever you want. Your device would then be running freestyle without warranty, fair enough for me as a first mockup. What's going to happen next is a handful of illiterate or unaccountable users will deface Apple's reputation by bombarding news sites with their misfortune. Apple would be cancelled overnight. I'm barely exaggerating.
Now I guess some EU negotiations could help to have some in-app purchases without fees (like buying a book in the Kindle app), avoid getting their app rejected for a shady reason (because rules can be changed whenever Apple sees fit) and, above all, allow me to set my morning alarm to some radio app (this one is ridiculous). The tragedy is that no "developers union" could ever succeed at this.
The last issue, about supporting authoritarian regimes, is probably the most difficult to solve. This is politics, there are no companies or governments that can have it all every time. China is a huge market: you cannot hope staying in business if you try to impose all your rules everywhere. That's the exact same idea behind having the EU make a stand on the single store issues. Also, the most intolerant wins [1].
[1] https://medium.com/incerto/the-most-intolerant-wins-the-dict...