We have almost all the technology. What we don't have is verifiability in most cases. i.e. the real problem is that the publisher cannot determine that the User Agent is telling the truth. Everyone has a different value on the value of their data. For instance, I find great targeted advertising to be practically like a recommendation engine. Instagram's ads are great! And few of them relate to things I've done on Instagram or Facebook. They're clearly 3rd party.

If we can find a way to ensure that the User Agent isn't lying (this may not be easy), then I could trade my data for a discount on the WSJ instead of paying full price and you could pay for the WSJ at full price and share nothing about yourself.

I think the truth is that most people will pick the discount, but that's because I would. I think that's a fair exchange and very open and clear. You can opt-in.