I agree that he should be alluded to for IM3. Have a scene with Stark and Hammer talking...
"You know Tony... it is an arms race to the end. Whether you are selling them, or trying to stop me from selling them... all we have is the process of trying to one up each other. You know the game... You were the best player. Now... I have to say that I find this new found nobility tiresome and somewhat misplaced. Look at you. Your gonna save the world??? With what??? More weapons... The best weapons yet, I might add. And you have to have known, that once we all saw what you have made, we would be right on your heels. You gonna stop progress Tony??? You gonna stop the world from turning??? Well, I am here to tell you that there is nothing that any of us can do to stop it... even if we wanted. There are things happenning that leave us no option but to find our own little place in the future. Really... you should see some of the things that my associate can do. It really is breath-taking. So com'on Tony... let's not waist each others time and resources, with all this... 'fighting'. That is for everyone else... and we don't want to fall behind... even the great Tony Stark could fall behind what's coming."