I just want to say, while the glitch should be taken with a grain of salt, I feel like implementing headshots for an FPS character is just the perfect amount of extra effort that Sakurai would put into the concept. It's so easy for me to imagine.
Also I can't remember if I ever voiced my support in this thread before, but I would absolutely love for Chief to join the fight. My confidence in him has been rising lately, and I hope that gut feeling ends up panning out because I think Master Chief is just about the most "ultimate" character we can get at this point. I have no strong attachment to Halo directly, but it's hard to ignore the significance and excitement that having Chief in the game would provide.
Not to mention, I really want to see more genres implemented into Smash. The lack of FPS in Smash is not only unfortunate from a historical representation standpoint, but also from a gameplay standpoint. These genres provide different ways of play, fresh new experiences that when implemented into Smash would result in some very unique new characters. When thinking about who to represent the genre, I can't imagine anyone more suited than Master Chief.