Avengers: Age Of Ultron - 32 Easter Eggs, In-Jokes And References

Thor's vision takes him to a doomed Asgard, where he encounters Heimdall (minus helmet), who warns of some extinction level event. Clearly this is a nod to the events of Thor: Ragnarok, which will see Asgard ripped apart by civil war (presumably by Loki disguised as Odin).

There were theories that the Ragnarok title might allude to the Thor clone built by Tony Stark, and there are other references that playfully nod to that possibility. 

First there's the mention of Mjolnir being coded to Thor's fingerprints (meaning only a clone would be able to wield it, naturally), and there's also the presence of Dr Cho's cradle, which could supplant the Stark technology that he uses to clone Thor in that comic arc.