Do you really think that's not so awesome of Disney to leave us thinking there will be other "Big Hero 6" sequel?! Anyway, being fan of this movie, I want to know why Sunfire is proposed. Since the eldest brother of Hiro Hamada, 14 years old child prodigy who now attends in San Fransokyo Institute of Techology. After many clues leading to possible sequel, I studied many people's theory of this Sunfire thing.
Hinting the sequel isn't enough for them, we need to know why Tadashi's body isn't found, then why he is dead, anyway?
According the rule of this original article, I agree. Why does that loophole needs to be open, leaving us to think Tadashi is actually dead? Tadashi's and Callaghan's coffin isn't there. It doesn't show anything. After knowing Callaghan is behind this fire thing, Hiro needs to know that Tadashi is alive out there.
Now back to the "Sunfire" point, I don't think Tadashi and Hiro will be fighting together, instead, they will be against each other. How's that even possible?
Let's think for second, Tadashi and Hiro are brothers, right? They are bonded, already. Is there any reason why Tadashi will fighting against his own brother, Hiro? He had suffered through horrible situation. Can you believe Tadashi is fighting against his brother and his own invention, Baymax? It's hard for me to believe that one of our beloved character will turn to menace.