Re: Who would you let Joss Whedon kill in Avengers 2?
That's why I'm saying I would expect it in the third, if at all.
Tony is the character we have/are seeing the biggest change of personality in.
Plus, Whedon does like to pull the metaphorical rug out from under his audiences (re: the "watch how I soar" scene in Serenity) and to have Tony go and put his life out on the line again, with audiences thinking 'Oh, we've seen this, he will survive', to end up dying...
I think Whedon could make it a very powerful scene.
Though, to be fair, you are correct: It COULD end up feeling like a re-tread.