I think it might be cool to have a button like we have for Wishlist which shows all the DLC for games that you already own which have unowned DLC for sale.
I know i could wishlist all of them. But I have noticed that sometimes a game randomly decides years after launch to put out a DLC. But because I haven't had a look at the game for a long time having completed it or whatever, I may never realise that new DLC has become available.