That's nearly identical to Apple basically did with the core technology fee in EU; 50cent per app install after a million which is free.
EU just fined Apple $500m for breaking the DMA and will be investigating the core technology fee now.
EU is mad for Apple figuring out a loophole in DMA. They'll eventually patch it, but overall the situation is unreasonable: Law is fluffy as hell and no-one knows what exactly is legal and what is not.
But in any case, this is not EU.
Also, it should be noted that a fragmented, chaotic, evolving mess of pricing models would be Apple's friend: more complex the out of store pricing is, potentially different model in every country, more likely it is for developers to just stick to well understood App Store fees.