The app owners will work with him to prevent AI training from taking data from the site for free. And any issues the third party apps have doing that will be shared by the official app. They're not special in that regard. You can't really have public secrets behind a paywall. It doesn't really work.
There are many, many options here that are only being held back by Huffman's ego. Imagine losing billions in valuation because of personal ego. I bet investors are thrilled.