Aaron Taylor-Johnson was the front-runner for the role of Joss Whedon's version of Quicksilver, but scheduling due to publicity for Godzilla wasn't clear. I say Joss Whedon's version, if you didn't know, because you'll see another actor playing Quicksilver in Bryan Singer's X-Men: Days of Future Past. Aaron Taylor-Johnson was able to get his schedule worked out and will now be free to film for Avengers 2: Age of Ultron.
Aaron joins Avengers pal Chris Evans in becoming an actor to don multiple tights, having played Kick-Ass previously. He still has one more hero to play to equal Evan's multiple roles of Human Torch, Captain America and that dude in The Losers. Avengers 2 will begin filming next year in London.