According to rumours out of Russia, of all unexpected places, the action in Marvel's upcoming Thor sequel is going to take place across all of the Nine Realms of the Marvel polyverse's Asgardian dimenson.
So that's Alfheim, Asgard, Hel, Jotunheim, Midgard, Muspelheim, Nidavellir, Svartalfheim and Vanaheim – a list I kind of want to sing to the tune of Tom Lehrer's The Elements* but it just isn't possible.
According to Kinopoisk, and reported at Coming Soon, a presentation at a Cinema Expo in Russia featured some Dark World concept art and a promise that all Nine Realms will show up in some way or another.
Alan Taylor, it is noted, has some experience with fantasy lands from his work on Game of Thrones. It seems to be implied that this means he'll ably cope with creating nine new ones, but I don't quite follow that logic any more than I'd assume he'd be bad at it because he also directed Palookaville.
Even if all of the Asgardian realms are featured, I can't imagine they'll all get a good chunk of screentime – this won't be some sort of cosmic road movie, I'm pretty sure.
My best bet, at the moment, is that all of the realms are shown in mourning – SPOILER ALERT! SPOILER ALERT! – after that major character, probably-possibly Odin, dies. Think of the celebrations when the Empire was defeated at the end of Return of the Jedi, maybe.
*Well, the Major-General song by Gilbert and Sullivan, but this way I can mention both.