I would be fully on board for this, but I think this decision comes down to Glow. We want to balance how much content we are adding to the server, so it doesn't become too much. This would have to start with his call.
Also, we would have to figure out the logistics to make it work. For example, the moderator skins require the moderator flag to get them. How do we allow you to purchase them during fourth of July, but be able to use it year-round. We can't use custom Flags oh, because we would run out of letters especially because most of them currently have a purpose.
One cool thing we can do is add a custom skin as the default skin during the holiday and then remove it when the holiday ends. For example, for July I could make a red white and blue camo skin that would look pretty cool, and remove it when July ends. It will be the default Terror skin for everyone, but it will disappear after the month ends. I know that isn't what you're looking for, but it's something that could definitely be done easily, with approval.
Sorry, just throwing out ideas.