True it would make it difficult to do third-party tracking across multiple sites (unless there was server-side information connecting your accounts, like an ema

True it would make it difficult to do third-party tracking across multiple sites (unless there was server-side information connecting your accounts, like an email address). And leaving aside browser fingerprinting. That could also just by achieved by disallowing third party cookies though - feels on the cusp of being a browser implementation problem (just stop allowing third party cookies).