Never had any doubt it would be great with Whedon at the helm....love that man.

Yes they do

Yup

<Small and I mean very small spoilers>

...

From what I've seen and read it went a little like this

DoFP was originally going to have the scene of Quicksilver breaking Magneto out of the Pentagon with a Young Juggernaut instead. There is a line where Wolverine says "I know a guy...he'd be a young man by now"....here's the thing, that line seems like it was kept when they decided to replace Young Juggernaut with Quicksilver as it makes more sense for Wolverine to know a previously established character then someone like Quicksilver who has NEVER been seen or mentioned before

Why did they add Quicksilver? Easy...because Joss Whedon announced Quicksilver and Scarlet Witch were going to be the Avengers. They were just starting to film DoFP so in my opinion it was at this point where they said to Bryan Singer "Look we want Quicksilver in our film, before he's in the Avengers"...makes sense since they'd want a character from the X-Men in their franchise rather then Marvels Avengers.

In the end it's pretty obvious that the Young Juggernaut scene was cut for Quicksilver, who despite the good, well shot scene everyone is talking about, he wasn't really what you'd expect Quicksilver to be like. I like to think if they went with the Young Juggernaut scene he would of been able to break Magneto out of the Pentagon quicker and they could of kept the Rouge plot they had to cut from the film. Juggernaut could of just smashed his way through and that would be that, plus getting rid of him would of been easier. I mean when you watch it you'll be like "Why did you not go with them", it's a big plot hole.

Sorry for the essay but....the more you know.