Generally, an API that Apple is developing gets dogfooded by Apple for at least a year before it is released for public use.
Sometimes they decide the API just isn't there yet, like Marzipan, and they put it through another year of revisions and dogfooding before they make it public.
Apple has operated this way forever.
I'm sure it takes some work on Apple's side to make that work for 3rd parties, but I'm also sure Apple knew that Spotify users (and many other music apps) wanted it and could have done it sooner.
>Apps adopt SiriKit by building an extension that communicates with Siri, even when your app isn’t running. The extension registers with specific domains and intents that it can handle. For example, a messaging app can register to support the Messages domain, and the intent to send a message.
https://developer.apple.com/siri/
Originally it only supported VoIP calling, Messaging, Payments, Photos, Workouts, Ride booking, Car commands, CarPlay (automotive vendors only), and Restaurant reservations.
The next iOS version adds SiriKit support for playing music.
Ever heard of FaceTime or iMessage? How about Apple Cash?
I am not super familiar with Apple Cash, but my understanding of it is that it also falls more on the Feature side and doesn't exist to provide a revenue stream on its own (hence why there are no fees for debit cards).
iTunes is clearly more of a product as it creates a significant revenue stream for Apple.
It makes sense that Apple cares less about competition with its features as that leads to a better user experience and more iPhone sales while Apple cares more about competition with products as that cuts directly into their income.
Just because Apple has operated this way "forever" doesn't mean that it isn't anti-competitive and deserving of attention from anti-trust regulators.
I'm not of the opinion that Apple should not be able to both operate and compete in a marketplace, but if they are doing both there need to be some rules put in place to prevent anti-competitive behavior.
No they couldn't. Because those APIs would become frozen and required by nature of large software vendors deploying software that uses them. Functional compatibility of an API which was documented as not finished would have to be maintained across OS releases.
I've seen unintended dependencies have a deprecation plan in macOS that takes years.
For the most radical example, there is still a copy of libssl.0.9.7.dylib. The 0.9.7l version came out in 2006. But it turns out OpenSSL does not provide binary compatibility even amongst patch releases.
This was likely why on Mojave, using "Marzipan" in your own apps required making operating system security changes (from recovery mode, no less).
Yes, they can. There is nothing stopping Apple from marking an specific APIs as "Unstable" with the understanding they could be removed or modified at anytime.