This is super cool. Was there any announcement or documentation for this?

We used a Cisco Meraki router once for a client and rigged it up to know who was in the office (for fun, to be aware that it could be done). It'd be nice to know the iPhone/iPad scramble themselves if possible.

Only if your phone is locked and it is looking for all open wifi networks. If you unlock it or it is connected to a particular wifi network this is not true.