Despite what the length of their privacy policies might suggest, first party sites are a lot stingier with their user data now than they’ve been in the past. The value of knowing who someone is and what they want is derived when you convince them to pull out a credit card, at which point you need to collect their data anyway.
Thus, I think we’ll see two tiers of data collection: Deep first-party info shared between retailers and data brokers to target advertising on their first party site, and less granular banner advertising based on privacy sandbox, taking the place of drive-by cookie drops. If privacy sandbox is as good for random blogs as industry is expecting (ie, not as perfect as third party cookies, but less impactful than Apple’s ITP was), I don’t think we will see a wave of email signups.