An Advertiser ID is the best method, especially because it can be looked up by multiple companies and is user controlled.
Unlike what people seem to think, adtech has been designed from the start for anonymity. The persistent ID is needed primarily for ad frequency and conversion tracking. Eventually identity is revealed when someone fills out a form or buys something but that's not necessary at the top of the funnel.
Currently: Advertisers can track you and estimate whether you are likely to buy the product.
This is good for advertisers.
If a user-controlled resettable ID prevents advertisers from doing this, what incentive do they have to not use their existing methods (in addition to the advertiser-ID)? Further, why would they not use tracking to say "Well, they reset their ID, but I know they're the same because of this other data, so I'm gonna link it back up behind the scenes."
Unlike what people seem to think, adtech has been designed from the start for anonymity. The persistent ID is needed primarily for ad frequency and conversion tracking. Eventually identity is revealed when someone fills out a form or buys something but that's not necessary at the top of the funnel.