The issue is that if Apple lose a tonne of money when Spotify decides to go flat fee, someone has to make up that difference. So smaller Devs lose out as they're currently being subsidised...
Free apps maybe, but then again the "all free" is a myth since there are costs to pay by someone, and Apple is free to keep subsidizing them if they so desire (because an entirely free app is good for their customers).
But non free apps with a smaller base you would be surprised I guess. Storage for hosting and GB for bandwidth is incredibly cheap.
To give a frame of reference AWS pricing is currently at $0.023 per GB for storage and $0.09 per GB for bandwith out.
That means 30% of a $0.50 sub is enough for covering the entire storage + distribution costs of one gigabyte for that user (and that's assuming you need to store an entire copy for each user, which you don't). Yes, there are other costs (website, review, ...), but then again how many subs are $0.50 ?
