I am noticing how OP quoted a PCmag article that the AT&T and Sprint model will not be sold as unlocked
I can't speak for the Sprint models but for AT&T- the policy at the Apple Store is that, if full price is paid, it is automatically unlocked out of the box
The genius reps (whatever you call them) probably already know this, but notoriously play dumb about it until an official unlocked model is sold
I do understand that this year, an official unlocked model is selling from day 1, but even so, we don't know how the apple reps will act. Some are knowledgable, and some just don't know what's going on.
Bottom line, if you want to play it safe and you want the AT&T version, get it, and request to sell it as "device only". Nothing at the Apple Store has changed, and I highly doubt that this will not work for the 6s launch.
Apple's unlock policies are standardized across the board, therefore I'm not worried about a thing.