But isn’t this how OSs have been historically sold? You bought Windows XP and were entitled to a set number of years of support in terms of security parches, etc.

Similarly if you don’t like the terms of the App Store you could have the option to purchase an open iOS v.1X and install whichever store you please. The only difference would be that you would need to pay again for subsequent versions of the OS, just like ppl would pay to update windows from XP to Vista to 7, etc.