Sure.

They’re either already not on Apple’s IAP (Netflix or Spotify) or they are very sensitive to optimising conversions, and would pay a premium to give users an easier option (which Apple is now incentivised to lower)

No one wants to own the payment instrument. That's useless, causes missed sales, and is a security nightmare. Companies don't reinvent their own Visa or Mastercard, for example, because that's a huge pain and the fees for using the existing products are low.

App developers were mad about Apple's egregious 30% cut for doing payment processing. If Apple wants everyone to accept Apple IAP, it can simply lower its fees to competitive payment processing rates.

> App developers were mad about Apple's egregious 30% cut for doing payment processing. If Apple wants everyone to accept Apple IAP, it can simply lower its fees to competitive payment processing rates.

Apple has never characterized the 30% as "payment processing" -- it's it's always characterized it as a commission, which the court affirmed and explicitly mentioned that Apple is allowed to pursue that commission, even if the developer chose to use another payment provider. Apple's IAP has been an enforcement mechanism for that 30% cut.

And before, they might not have bothered developing an app, or one for iOS. Now you have choice. Choice is good.

What big names haven't developed iOS apps but may do so now? I'm hard pressed to think of any. They may not always allow in-app purchases, of course, but they generally exist.

Well. Fortnite for example.