Most of the recent Marvel movies have offered up decent versions of the characters in Avengers - Age of Ultron in their respective figure lines. There are versions of Black Widow, Nick Fury, Black Widow, Thor and War Machine (provided he plays a role in the film) that would all be reasonable figures to reissue if Hasbro had moved forward with a fully articulated 3.75" figure line. And this new version of Iron Man is a good representation of the new Mark 43 armor.
So who does that leave? Hawkeye (new look), Captain America (new uniform), Hulk (not done well previously), the twins, Ultron and the Vision. All told, it wouldn't have been that crazy of a line to build had Hasbro pursued it.
I agree - would have been awesome to see them make a MCU Ultron in the Infinite line style...