Good news! I was calling AT&T to cancel an old iPad mini and my dad's cell phone off the plan (should have done this a few months ago). At the end, I asked, "hey is there any chance that I can get an early upgrade on my iPhone? I bought a 6 on contract last year."
After looking into it, the contact said that by calling, I can get an exclusive deal not available in stores by switching to one of AT&T's Next plans. Even though I'm only 12 months into my previous contract, the old iPhone 6 is mine to do with as I wish (to the wife...until she's eligible to upgrade from her iPhone 5s). So I have an iPhone 6s+ on order!