What does "you generate the metadata" mean? If an app on my phone "generates metadata" I own it under this principle. Likewise for code running on my computer.
Your phone/os generate raw inputs (eg touch events in the format of: posx, posy, pressure). Each app then make use of these raw inputs in its own way. SwiftKey will give you some words. Piano app will pay a sound. And So on.
Interpreting and converting these raw inputs into what a user wants, is literally what an app gets paid for.
It's a simple principle, but since it makes the world shittier, let's not adopt it.
This would enable a black market for the data, at which point good luck regulating
Are you saying that this doesn't already exist? There are tons of people selling passwords, profiles, credit cards info, social security numbers et cetera. Or are you trying to say that legit companies will begin doing that? Aren't they already doing that too? Facebook and Cambridge Analytica being just one example that we know about.