This idea has been merged into another idea. To comment or vote on this idea, please visit PL-I-508 Campaign price flexibility: stacking, category based, set prices.
Today you select which products to include in a discount using a product list or point out specific products. A common scenario is to discount all products in a category instead. You can achieve the same result using smart lists, but after a while you end up with too many lists if you have many categories.