Jaimie Alexander, who plays Sif has been making the rounds during the promotion of Thor hitting DVD/Blu Ray. She talked to MovieWeb mentioning a few things she'd like to see in the sequel. Which includes a romance between Sif and Thor along with the addition of Beta Ray Bill.
"Yes. I would love
for that (romance) to happen. I don't know what the story is going to be
just yet, and nothing has been made official, but the hope is that it
will be made official, and I would love to explore more of that. And, in
future endeavors, I would love to see Beta Ray Bill, or something like
that. I think that would be really cool. Like you said, there are so
many avenues to go down, so many endless possibilities."
Also, Tom Hiddleston talked to Collider about Thor 2 and he gives the impression Marvel could be expanding the cosmic world and exploring the other realms. I've been hoping the second film would be entirely set off-Earth and this seems like another possible step in that direction. Previously, Hiddleston teased that Loki could end up fighting alongside Thor in the sequel. That angle has been hinted at for Avengers as well. I think Loki is an excellent character but he needs a limited role in Thor 2 if only because he's been featured in two Marvel films within the year.