look at this pic. its not gonna be too hard to shuffle Avengers in and out anymore. its not the initial team-up and theres no element of the distrust of Nick Fury. Falcon, Wasp, Ant-Man may be recruited with no muss and no fuss whatsoever. Easy peasy.
The Avengers, as a team, are ready to go. So Avengers 2 can focus on a threat big enough to overtake them. Now I've been pro-Ultron for quite sometime now. Even before that I figured it'd be Thanos. So I'm pretty much open to many options. I'm just wondering how it might go if they tried for Masters of Evil and gave us a taste of the team led by each Zemo and Ultron.
Mandarin has the right idea, and Whiplash before him. These heroes need to be taken out before they band together and destroy their way of life. It makes sense that they would band together for the greater bad. :P