I have no idea if this has been said before, but whatever here I go XD
I would think it would be fairly cool if your vault from shelter was generated into fallout 4. Obviously in a designated spot, and declared non cannon. Perhaps only accessible through wacky wasteland traits or something similar would be a very cool easter egg, and perhaps some sarcastic comments on generic actions of the vault you over saw. I personally would think since its built in such a generic way implementing it as a bonus into the game would be kind of amazing.