Nothing will change for you if you don't want it to change. This is only an option for people who want additional functionality. Nobody is forcing freedom or change on you by adding one more hard-to-find option buried in a menu somewhere for people who really want it.
The common concern is that critical software that users depend on will only be released in a way that circumvents the safety mechanisms that Apple employs to prevent the execution of malicious code. Is that fear unfounded?
Even setting aside the malicious code concern, many users don’t want to have to track several different app stores to find functional software. What prevents this from becoming the case?
Yes, either they have a strong sandbox model or they don't and the appstore won't help either way.
> What prevents this from becoming the case?
Same as in real life, you can buy products at different supermarkets...
Most generic stores have everything though.
> Are there any examples of critical software that users depend on only being released in a way that circumvents Google's safety mechanisms?
Chinese Android phones are riddled with spyware.
https://gizmodo.com/android-xiamoi-oneplus-phones-personal-i...
I don't think there's a danger Apple will discontinue the App Store in any region as a result of these rulings.
That's not true. There's always cost, even for a feature that you personally never use. Sideloading opens tons of new security attack vectors and dark patterns, that it's going to affect absolutely everybody eventually.