I created a sticker pack extension (not the full sticker app) for iMessage using Xcode 8. I have the icons too and the project gives no errors or warnings. I registered the bundle ID, archived and uploaded the archive, and created a new app. However, I don't see anything about stickers!! iTunesConnect seems to be treating it like a normal app.
In the Apple tutorial, it says there's a category called "Stickers" that I can give it but I don't see that either:
Category. You can list your sticker pack in the Stickers category or another category that best describes your app. You can also list it in a second relevant category.
You cannot upload your sticker pack to the Messages App Store yet.
Apple will tell you when you will be able to upload Stickers to the AppStore. This is normally right after the Keynote Event. Take into consideration that in order to upload an App to the App Store you have to use a NON Beta Distribution of Xcode.