"here’s a bunch of reasons why this might not work, not least that no-one except Google and Apple want Google and Apple to have that much control over publishing and advertising. "
I've said this previously, if you for a second think Apple is protecting you against evil "Social Media company" or "Evil X Advertiser", you are wrong. Apple is only looking out for Apple. And they want to be the one who controls user data. Plain and simple.The enemy of your enemy is not necesarily your friend.
Things SHOULD change. Moving the power from one big corp to another big corp is not the answer. No matter how convenient it may seem.