I was reading an article on here (http://moviepilot.com/posts/3797840) by Zane Sanders, and wanted to add a to it.
During Zane's very well written post, he discusses what we know about the Infinity Stones so far in the MCU. He very accutely describes the 4 we know of (Space, Power, Reality, and Mind) and theorizes on the the 2 we do not know yet (Time and Soul).
The Soul Stone caught my attention as Zane mentions that Heimdall may be the owner of the Soul Stone, which makes perfect sense seeing how he mentions in Thor: Dark World he can see 10 trillion souls.
Then, for whatever reason, it hit me. This image from Age of Ultron
Why are his eyes missing in the flash from this scene? My theory: Heimdall's eyes are the Soul Stone!
During the Ragnorok, the MCU adaptation may be Thanos showing up and laying waste to Asgard to take the Tesseract and the Soul Stone. Which would put a cosmic level threat in full effect for the audience to see.
This would also be a great way to show Thanos' power. We've already seen the Dark Elves attack Asgard with little collateral damage. When a single being can be shown to decimate the entire city as well as killing several Asgardians.
Again, this is all a very thin theory, but I had to write about it and get it out there. If there are any of you that agree, let me know in the comments. Be sure to check out Zanes article too http://moviepilot.com/posts/3797840.