The Soul Stone

Prior to its release, the biggest rumor was that Thor: Ragnarok would reveal the Soul Stone. It was suspected that the Stone was hidden behind Odin's eyepatch, and was the source of the power that kept Hela at bay. That wasn’t the case.

Returning to the Eternal Flame thread, Hela says that it’s true power. That’s quite surprising, especially since she also says that the Tesseract is not bad. So Thor: Ragnarok may have debunked the Odin rumor, but it also opened up another conversation.

Is the Eternal Flame the Soul Stone? It could be, but if it isn't, we can bet that the last of the Infinity Stones will turn up in Black Panther.