The recent appearance of lady warrior and Thor flame Sif in "Agents of SHIELD," a TV series whose storyline is linked with the Marvel Cinematic Universe gave rise to many implications for the third Thor installment.

The opponent that she was chasing also points to some possible cast rumors based on the characters.  The episode, "Yes Man" is the fifteenth in the "Agents of SHIELD" series. First, the episode synopsis from IGN:

"Lorelei's introduction alone is notable, of course, for her place in Thor's history and beause she is the Enchantress' sister - a character many are hoping to see in the Thor movies down the line. Also, Sif's throwaway line about Odin wanting Lorelei alive at the end is way more notable when the end of Thor: The Dark World is taken into account. Wonder what plans "Odin" might have that he needs Lorelei for, hmm? Then of course was Sif's quick rundown of every blue-skinned alien race she'd encountered, which included the first MCU mentions of the Kree and many more. Oh, and we had Coulson tell Sif he wanted to tell Thor he was alive himself, helping to underline that no, not everyone (notably the Avengers) knows he's back."

("Thor: The Dark World" Spoilers Ahead)

The interesting detail about Lorelei is that "Odin" wants her alive. At the end of Thor:TDW it was revealed that Loki was sitting in the throne using his shape shift ability. Why did he want Lorelei alive? It's either he's going to use them in the future or he might have been the one to send her in the first place.

Sif mentions the Kree, one of the most important alien races in the Marvel Universe. The Kree was the main alien race to oppose Thanos, and their introduction would imply that Thanos is indeed coming to the Marvel Universe.

One more detail is that Coulson has asked Sif to tell Thor that he was alive which means that it was top secret even to the Avengers. The Avengers and SHIELD have not been connecting well lately, and it's not because they have a lack of technology.

Asgardians are starting to show up at Thor's beloved Midgard-and you know which Asgardian hates Midgard the most.