actually you can do it as long as you don't mention about cheaper alternatives anywhere within the app.

Huh, do you have a reference to the guideline that says that?

Older versions of the app review guidelines allowed apps that could access content sold outside the app store ("reader" apps) to dodge the app store commission if their in-app content was provided "at the same price or less than it is offered outside the app store" (formerly section 11.13 of the guidelines).

Here's a 2011 article about Apple revising that policy: https://appleinsider.com/articles/11/06/09/apple_backs_down_...

Hmm, I wonder if Uber/Lift could have a system where you either have an iOS account or an Android account. So then whatever you buy on Android wouldn't be transferrable to iOS. You could switch your account between the operating systems but your subscription wouldn't transfer.

Dropbox and Youtube Premium do it already.