I'm flying from AUS-CUN on Wed, April 4th. I was curious what dictates whether or not the electronic check in offers an upgrade available for purchase. Most recently, in November, my mom and I flew AUS-ORD-STL, and were offered the ability to upgrade to First on the ORD-STL segment. According to aa.com's Available Seats, only 5/22 are booked right now. Of course, all the AAdvantage elites upgrades must clear, but on a leasure route, I'm hopeful. Would this flight qualify (Flight 2063 DFW-CUN only) to be offered as an upgrade at the airport? What are the criteria/odds?