I think a rag quilt with regular cottons vs flannel would be fine. Would you want to include a lot of white since it's a late wedding gift? Or even a log cabin/rag quilt? You could combine the simplicity of log cabin, and the speed of ragging the blocks? Since the log cabin was thought to signify hard and easy times with the light and dark of each individual block...
Good luck no matter what you do. Remember you have up to one year to give a gift for a wedding.