Which newspaper's app would the newspaper:// URL link to? It's certainly possible to do this, but it's often done badly. And if the app doesn't display its URLs, and they're not made available nicely in its "share" functionality, then the user isn't going to be able to work out how to refer to the article.

Also from that link: "Security considerations: Unknown, use with care." Great!

(news:// is already taken by Usenet NNTP to refer to articles by ID)