Earlier quoted context omitted.
Nonsense. I'm using WYPopoverController[1] in some of my apps and they're a-ok. On the component's page they even have links to apps in the App Store that use it[2]. [1] https://www.cocoacontrols.com/controls/wypopovercontroller [2] https://itunes.apple.com/us/app/cookapp/id771313730?mt=8&uo=...
Whether they have removed apps that use is irrelevant. That they can at any point remove them because of their policies but don't should not be lauded, it just creates an air of confusion that they can use to their benefit as they see fit.
The fact remains that there are plenty of documented examples of Apple tossing apps from its App Store for reasons that amount to little more than corporate whim or gatekeeper prerogative, or for no adequately explained reasons at all.
Should Apple ever decide that its popover API is ready for prime time, it could yank all apps that do not use it and demand that the Apple popover be used instead. I seem to recall something similar happening with third-party apps that improved upon the native camera API, but my memory may be suspect.