Entropy that changes when your local IP does? That's worse than useless for ad targeting. Even if it were useful, I don't think there's much of a chance that adtech companies will build out STUN servers to handle the kind of traffic they do just track down the 0.001% of users who do not accept third-party cookies. Can you even do WebRTC from an iframe?

Browser fingerprinting is absolute FUD. It makes no sense for advertisers, and it's pretty useless for anyone else, too. Every time I visit the EFF site that checks my fingerprint, it tells me I'm still unique. That's perfect anonymity!

Revealing a user's personal IP when they're using a VPN is a real problem, though, where the computer isn't doing what an even an experienced user would expect.