I just had a thought, and I don't know how I feel about it ethically.
Right, so imagine a free game.
Good game, you play the game, it's a fun game.
But, you can buy DLC. We'll say there are 4 expansion packs (picture Blood and Wine, Hearts of Stone, etc). In each of these is a thing you can find, like a secret key.
If you get all 4 keys, then you can unlock a secret expansion pack. And it wouldn't be advertised anywhere. It would be a total secret (until the internet grabs a hold of it of course). Kind of acts as a little gift to the people who supported the game from the original through all the DLC.
Naturally I can see people getting mad at it, but I feel like this would be a pretty cool thing to do. What do you guys think?