With the introduction of iOS 10 Apple is also introducing iMessage apps (extensions) and sticker packs. This is a category in which there is going to be a lot of new developers/designers/illustrators, new to the Apple ecosystem at least.
The main reason for this are data protection rules around the globe and we’ve written extensively about additional reasons in our guide for iOS apps. As of a couple of days ago, Apple has also updated their App Store Review Guidelines to incorporate language for stickers and iMessage extensions.
In section 5.1, the privacy section, you’ll find: