AdExchanger is asking whether identity infrastructure should move server-side.
I'd ask a different question: why are we still trying to stitch user paths together?
Server-side is the same circumvention we've watched for years. Fingerprinting, identity linking, now this. Apple tightening Safari is a browser saying enough is enough.
Walled gardens stopped allowing user-level tracking as far back as 2016. That's 10-plus years. Safari removed third-party cookies first, and the workarounds have been chasing it ever since.
The clients who aren't worried right now stopped depending on user-level data a long time ago. A Safari change doesn't touch them.
The ones who will get hurt still think the web is a user-level tracking machine. It hasn't been for years.
A server-side rebuild of the old model doesn't make you right. It makes you confident about a path you can only partly see.
Measure at the aggregate level, aim to be less wrong, and stop paying to rebuild a view that's already gone.
Responding to The Server-Side Escape Plan; A Lament For The Dead Internet, AdExchanger