What "trilogy"? Feige has shown no indication whatsoever that he's interested in limiting the Avengers (or anyone else in the MCU) to a trilogy. He's not even limiting a franchise to the number of films that any given actor is signed for....he's already said that characters will be recast and continuity will remain intact --- even for Iron Man, post-RDJ. Also, the Avengers has just painted a four-color universe, old school style. There's no need to Nolanize the Avengers to make them grittier and darker. And even though Thanos is a mass murderer, his presentation in the comics by Jim Starlin has always been more Jack Kirby than Frank Miller. Let's leave "dark and gritty" for the street-level crimefighters, where it belongs.