at the moment I'm thinking Iceland battle might end up being a flashback scene with Thor and Loki (Warriors 3 and Sif probably too) vs Malekith and Algrim and the Dark Elves in the past. It seems a bit much for it to be Thor vs Malekith Algrim/Kurse AND Loki and again it seems likely to be a short scene based on the on location filming time.
Yes it is similar to Odin vs The Frost Giants in Thor 1, but this could accomplish a few things at once.
1) potentially show how Malekith got messed up and what he is vengeful about (which I think will need to be shown for the GA)
2) potentially they could have Algrim fight Thor and be betrayed by Malekith as he is in the comics there, and then be returned years later all Kursed up. This may make more sense to do with the pacing for the movie, and explain why Algrim/Kurse doesn't appear to be present during the Greenwich fights.
3) Show Thor and Loki fighting side by side as they had in the past, which at least some of us want to see more of and may be important to the story arcs to remind people about that.
4) Potentially we could have Thor vs Algrim and Loki vs Malekith which again at least some of us want to see, and seeing Thor vs Malekith twice in one film is apt to be too repetitive.
5) Potentially show us Svartalfheim
As I posted in the regular news thread, I'm leaning towards the Stonehendge scene with the news reporter being a scene at the end where the reporter is reporting on whatever just happened, not unlike Avengers, and there is a scene where at some people are returning to the "old ways" and worshipping Thor.