Yesterday it was announced that Marvel VP and producer Craig Kyle would be co-writing Thor 3 with Christopher Yost. It's looking like the third film could follow the Ragnarok storyline. HitFix has a source close to the production that claims this is the direction that the next story could be headed, and that it would be teased at the end of Avengers: Age of Ultron.
"More importantly, if my sources are correct, the end of "Age Of Ultron" sets up a difficult situation for Thor as Midgard and Asgard find themselves looking at a possible war. Could we be looking at the beginning of Ragnarok, brought on by Loki in the guise of Odin? Could the third film find Thor having to fight against the realm that he's spent so much time defending?"
It's hard to put confidence in this source since we really have no idea who that source is, but Kyle himself has previously talked about a possible future story arc for the third film, and even hinted at Ragnarok. He talked about all this stuff during a set visit with several websites, saying,
“This is Hall of Science again, another place you’re going to see today. This is gonna be a pretty neat spot that we actually get to explore, which will go into the various breakthroughs and discoveries of the Asgardians where you’ll see functioning models of the Big Bang and all these wonderful technologies that no human has ever laid eyes on before.
"And inside’s gonna be this living tree, which we believe is connected to Yggdrasil, the cosmic tree. And the effects and woes and success of the universe are spoken through this, this living object. So, should the end of all things ever come this would probably be the first thing to fall. And we have a really tremendous scene in here with Thor and Odin.”
When "The end of all things" was brought up, Kyle was asked if he was talking about Ragnarok and he replied,
“It’s one of the bigger stories, right? [LAUGHS] So, who knows? [LAUGHS]“
For those of you not familiar with the story arc, Ragnarok is an apocalypse of sorts that represents the end of Asgard. Ragnarok is an apocalyptic-battle that the Realm of Asgard has experienced over and over and over again. Ragnarok is a cycle of death and rebirth. It comes in cycles, randomly killing gods and restoring new gods with no knowledge of what took place. This is happening in an effort to sustain Those Who Sit Above in Shadow, which are celestial beings that are the gods of gods. They need this cycle to continue in order to survive. Thor is eventually made aware of this cycle and it pisses him off, because it robs his people of their glory and memory. Thor vows to restore his people's glory by ending the cycle. This will require Thor to form an alliance with his arch-nemesis Surtur. You can read more details about the story here.
In Norse Mythology and in Marvel Comics there are fallen warriors called the Einherjar, who spend their death feasting and continually fighting. They are waiting for the day of the Ragnarok where they can fight for Asgard once again.
This would make for a pretty epic storyline, and I hope it's the one that Kyle and Yost are bringing to the big screen!