I, like every other fan of the Marvel Cinematic Universe, was intrigued to see the new concept art for Avengers: Infinity War depicting Thor alongside Rocket holding a weapon that does not appear to be Mjolnir. I started thinking about what reasons could exist for Thor to use another weapon and a couple options came to mind. But when considered with some of the other rumors and theories floating around along with what has been confirmed by Marvel at this time, one conclusion/wish came to the forefront: Someone (most likely Thanos) destroys the Hammer to take what even Thor didn't know it contained - the Soul Stone!
WARNING - This contains speculation and potential spoilers for upcoming MCU movies.
First, a reminder of how Mjolnir has been described in the Marvel Universe...
"Forged in the heart of a dying star, its power has no equal, as a weapon to destroy or as a tool to build. It is a fitting companion for a King." - Odin (Thor, 2011)
(Thor's Coronation Ceremony; Thor)
Mjolnir was described as a weapon with no equal by a man who is fully aware of the existence and power of the Infinity Stones. He doesn't even dispute that it could be used to destroy another Infinity Stone (Aether) in Thor: The Dark World. While Asgardians are very advanced, I doubt they are able to forge something on that kind of power level unaided; that would put them in the same league as the Celestials. However, as the Scepter and Ronon's hammer proved you can embed the Stones inside of weapons to greatly enhance their power. Having the stone inside of Mjolnir while forging it would have both made it a very powerful weapon, and helped to keep the stone safe. It would be in the hands of Asgard's best warrior encased inside of one of the strongest metals in the Universe.
Thinking more about the powers of Mjolnir, it makes great sense to have the Soul Stone inside of it. Aside from it's raw strength and power, it's most notable in the MCU for it's bond with Thor and ability to sense to 'worth' of those who attempt to pick it up. Asgardian magic is of course partially responsible. However, it's ability to sense Thor's presence and travel to him over vast differences (remember in The Dark World when Thor went through the portal the hammer traveled into space towards Thor's location at the time) would be easily explained with the Soul Stone being the source of that bond. As Doctor Strange showed magical abilities can be used in conjunction with the Stones so Asgardian enchantments could harness the Soul Stone's power for their purposes. It's also worth noting that as useful as these abilities are, no other Asgardian weapon has demonstrated such a bond with anyone.
(Mjolnir in space; Thor: The Dark World)
It is also worth mentioning that while the THANOS stone theory is not officially a fact, this would fit within the theory. Though I didn't buy it initially, the theory has held up pretty well for the first 5 stones and seems to be looking pretty good. Even if Marvel didn't initially intend for this, I'm betting they're aware of it and willing to follow through for the sake of the fans.
("Hammer" would complete the acronym)
Above was where I wanted to make a case that Mjolnir could/might contain the Soul Stone. Now here's where we get much more into speculation and what I would like to see. We've all seen the handle of Thor's weapon in the concept art for Infinity War that looks not too much like Mjolnir (though the wooden handle itself does look similar) and wondered.
We've already seen Thor lose his hammer once due to being 'unworthy', so I think him losing the hammer for a reason like that would be a major step back for his character and just not something the audience would want to see. Mjolnir being destroyed on the otherhand could be much more interesting, as Thor would have to deal with the loss and grow as a warrior and a character. This would be very difficult for anyone or anything to accomplish.
With Infinity War approaching, Thanos has not yet gotten to establish much of a presence as a character to be reckoned with yet, and won't in the other movies in 2017. What could be better for showing the threat that Thanos would present and set up the audience for Infinity War than if at the tail end of Thor: Ragnarok following the final battle as a tired Thor is looking over what remains of Asgard, Thanos strolls in and completely manhandles Thor. Then with Thor laying on the ground he desperately calls Mjolnir to him, and as it flies past him along the ground Thanos smashes it under his boot! This would be the reveal of the hidden Soul Stone, which Thanos would scoop up with the Gauntlet leaving Thor as broken as his home and hammer.
(Broken Mjolnir; from the comics but not sure which)
Eventually Thor may use the remnants of Mjolnir to forge a new weapon- closer in appearance to the Ultimate Mjolnir- which is what he uses going forward. This could perhaps be a post-credit Black Panther scene with him getting it forged in Wakanda while warning Steve Rogers about the coming threat of Thanos. There would also be the story potential for the stone itself to maintain it's connection with Thor, allowing him to sense Thanos' whereabouts and perhaps try to call the Gauntlet to him if Thanos is weakened at some point in Infinity War giving them a potential path to victory.
What do you all think? Did I miss anything supporting or disproving this? Feel free to comment below!