As far as I'm concerned, Mac openness is just a cat that got out of the bag, before anyone knew they could produce a _mint_ from rent seeking walled garden platforms. I find it highly unlikely Apple is not looking to correct this mistake on Mac, even if it's done so gradually that by the time the pull the trigger, no one even bats an eye.
I would not be shocked however if at some point they switched to developers having to buy special Macs to have this capability, and normal Macs would cease to be able to turn off secure boot and SIP and would require code signing/store distribution universally.
[1]: https://developer.apple.com/programs/security-research-devic...
A ragtag band of devs all banned-for-life from Apple’s stores could put together a new app-engine or game-engine that other devs use as the basis for their app and provided that those apps don’t break the rules about undocumented APIs or malware (and no-one in Apple’s higher-ups gets suspicious...) then those apps will appear. I don’t believe Apple has any way to automatically ban or delete all apps that use the same third-party libraries by using their macOS Notary system or iOS Certificate revocation system - they’d have to inspect every published app-package individually (granted, this would be automated, but you know what I mean).