We did something similar on Philosophy, where we designate one philosopher each week, and each person who asks a question relating to that philosopher is eligible to win a prize. It's gotten a positive response so far, and we could easily adapt the model to photography topics. Everyone who asks a question about a given week's photo topic is entered into a drawing to win prizes.
Some example topics are bags/cases for carrying your photography gear, various options for displaying/presenting photos, flashes and lighting, macro photography techniques, nature photography techniques, etc. A great way to start would be to think about topics that are popular during the holidays and begin with those.
What do you think? If you have suggestions for weekly topics, please leave them here as well!
Edit: See below for my suggestion for the first week's topic; let me know if there are any concerns or alternative suggestions.
[Note: This contest would run on the main site, and the goal is to generate questions and answers about topics that we don't cover as much as we'd like, or topics that we think will be very popular in the coming weeks or months. We're working on a separate contest that would take place on meta and encourage our community's creative side, so stay tuned for that later.]