1. Spider-Man
Let's get this out of the way. There's not much chance of Spider-Man appearing in Marvel's Agents of Shield. In fact, it's probably zero. Sony owns the rights to all live action Spider-Man, including live action TV, so that is why you'll see Spider-Man cartoons by Marvel and Disney, but no live stuff coming out of the studio. It's painful because it makes so much sense. New York is Spider-Man's turf and in the comics, he always seems to have a close relationship with the SHIELD team. Spider-Man is such a compelling character because he's not over-powered. There is a level of threat when he walks into every battle and that means there's a level of humanity you don't find with, say, Superman on the DC side. To see Spider-Man onscreen zipping around skyscrapers in Agents Of Shield would be a joy, but that's a dream that seems at the very least, a long long way off. The only way to get Spider-Man back to Marvel would be if Sony sold the rights. And that would mean that Spider-Man would have to be no longer profitable. Try and organise that worldwide boycott of The Amazing Spider-Man 2.