Sit down, kids, and let the director of The Dark Knight Rises lay out for you what is and isn't acceptable etiquette if you want to be a "real" movie.
Filmmaker Christopher Nolan, speaking with The Guardian about his upcoming film Interstelllar, took a shot at Marvel Studios' post-credits sequences, reportedly saying "a real movie wouldn't do that" when he was asked whether he and Zack Snyder considered such a scene for Man of Steel.
Of course, the way The Guardian phrased it -- a "comedy ending coda" -- implies that it was a throwaway joke a la the Howard the Duck piece in Guardians of the Galaxy, rather than something serving the film or sequel in the vein of...well, just about every other Marvel movie. Still, it's likely that distinction wouldn't change Nolan's mind much.
You never know, though: maybe it really was all about the "comedy" part of the question. After all, there's supposedly a "no jokes" policy at playon the Warner/DC movies.
The director faced persistent questions about whether there might be such a sequence in The Dark Knight Rises leading into Man of Steel, or in Man of Steel teasing what would be next. He always denied there would be (and obviously there wasn't), but hadn't made his disapproval of the very concept explicit before.
Interstellar opens on Friday.