Anybody have references to the technical details behind this change?

One way I can think of would be to use ETag headers, which are intended to be used for caching but can be abused for tracking purposes[1] since by definition the browser is required to send back the server-provided ETag value.

Alternatively (or additionally), browser fingerprinting[2] seems like the perfect candidate technology to replace cookies for tracking purposes, since it can't easily be "cleared".

[1] http://en.wikipedia.org/wiki/HTTP_ETag#Tracking_using_ETags [2] https://panopticlick.eff.org