So I was thinking about this SIM thing. So in theory if you take your At&t SIM out, and just use the phone on WiFi, you should get the update right? That is if you believe its the SIM that dictates the update. I for one don't understand why my unlocked Nexus 6 is bound to the same rules as a nexus 6 under contract with At&t. That is the point in buying unlocked right? You don't have to deal with a lot of the carrier bull crap.
That's what I assumed in theory too.