This is how I see it happening: someone in the IP suit, likely controlled or hired by Mandarin, makes Tony the bad guy in the public eye (via set-up or blackmail, whatever). Maybe even beat him badly in public, thus resulting in injuries and then he turns into his alcoholic addiction. It turns out the guy operating the IP suit is actually infected with the Extremis serum that Killian provided to him, also being controlled by Mandarin. In the end, Stark conquers his alcoholism problem and merges with the Extremis nano tech to his body and then defeats IP. Then teases the Avengers 2 future villain.