Yes, Southwest does occasionally offer challenges, sometimes for A-List, sometimes for a Companion Pass. They are usually very narrowly focused on specific markets, destinations, or a group of flyers that don't have any obvious similarities. I personally wouldn't count on getting a promotional offer before the end of the year so if you you're short a few flights start making plans to get a few extra in before the year is over.
BTW, the offers come via email and are also listed in your account online under the Promotions section.
