Empire recently conducted an informative podcast interview with Joss Whedon. The Director gave insight on Loki not being in the Avengers sequel, the first draft of the script, Scarlet Witch and Quicksilver and how they'll fit into proceedings to the current state of the first draft.
Whedon's comment about Loki not being in the Avengers sequel:
"Everyone is going to be looking for the Loki-Hulk smash moment and you'll be looking for [a quim moment]. First of all, imitating what I did before is the surest way to do it not as well. Second of all, Loki's not there to say those terrible things. Although I do think we should bring the word back, not as an insult, it's just a nice word."
The first draft of the script:
"I've turned in a first draft. The story is very set, everybody's on board with the exact movie I'm trying to make which is what worked the first time. I said, 'I want to make this movie, a Marvel version of this movie.' And they said 'Yay' and never looked back. Well they said 'Maybe the tone' or 'Maybe this structure' but once we had it, we had it. And I feel like we're there with Avengers 2 which is really important."
"There's still fine tuning to do on the script. There are many things that can be 'plussed' and be better and also, there's some science in it, which means I have scenes where someone says 'Science the sciency science'. So I'm like, 'I'll fix that later.'"
How Scarlet Witch and Quicksilver fit into the script and as for the Quicksilver issue - which has got more complicated now that Fox have put the same character into X-Men: Days Of Future Past - Joss Whedon has this to say: "He's in our movie and he's going to be dope."
"Quicksilver and Scarlet Witch are very close to my heart because they were Avengers the whole time I was reading the book as a kid. Sometimes they were evil but sometimes they were good. They're very... textured, they're very different from everybody else in the mix. They're not there to make things easier on The Avengers but what we do with the group once we've got them is squeeze. The fun I'm having doing that is probably unseemly."