It's possible. Unlikely, but possible.
I've been upgraded before into or out of ATL over the years as an FO, including major cities like BOS, MSP, and DCA at one time or another. My highest batting average is a flight to or from CLT (big deal since it's a 40-minute flight, but an upgrade is an upgrade), where I'd say I'm at about 40-50% success. Speaking of which, I got upgraded at the window tonight for a Saturday afternoon flight CLT-ATL -- which was V8 as of this afternoon.