Right now there is a sale on EGS and it would be nice to have a filter so I would only see deals for games that are not on Steam. I will only buy a game on GOG or EGS if it's not available on Steam because I like my game library to be as consolidated as possible. I think many people would find this feature useful and it might not be hard to implement since it seems you already have the data for each game, store, and platform.
