Going from Kickass to Quicksilver isn’t that big a leap. Especially when viewed in context of Johnson’s other work. Johnson’s performance as a young John Lennon in Nowhere Boy is pretty close to what you’d need for a convincing Quicksilver.
This story is even more interesting when viewed in context of the fact that both Marvel and Fox have rights to the character and he’s going to be appearing in both the Avengers 2 and X-men: Days of the Future Past.
It’ll be interesting to see which incarnation is closer to the source material. I’ve got my money on the Avengers 2 incarnation because the chief problem with the X-men movies is that they dump nine thousand of them in one movie and just hope for the best. I counting on Quicksilver getting a Colossus style X2 cameo.