So basically my alternate ending wouldn't really change anything of the movie itself, but what's after the movie, ya catch my drift?
So, in my version of the post credits scene, we would have instead had a scene showing us a still breathing Tadashi who was blasting fire out of his hands in his rage, because he's trapped in a laboratory. Then, a taller man in Samurai armor says to him, "SunFire, it won't get you out of the project, so it's basically pointless." Tadashi then looks up at him and says " I know Silver, but I've got to get back to them, to warn them, to help them."
So in a nutshell my [Big Hero 6](movie:425271) post credits scene would tease 3 new characters, SunFire, Silver Samurai, and hopefully Everwraith.