I think if what youre selling is just app based content apple could sue and force an audit. Like if the product is just a subscription to the mobile app they could claim that all revenue received from that is subject to the fee. But if youre selling a more general subscription that can be used on different platforms I think this would work.
If that messaging is allowed, it is a huge change from before, where external links for taking payment was not allowed at all within an app. A lot of users will probably opt for the 27% discount if given the choice.
I don’t see anything that prohibits this: https://developer.apple.com/support/storekit-external-entitl...
Apple cannot (or, per antitrust law, should not) tell a developer how to design and sell their merchandise in their web based storefronts.