My predictions:

- Hydaelyn will be revealed to not be as pure as righteous as her devout servants believe her to be.

- Zodiark will be revealed to not be entirely on board with what the Ascians are doing in his name. He will also not be the cackling villain some believe him to be.

- Elidibus will become an ally after being betrayed by Solus. It will be revealed that his concerns in regards to balance have merit but that there is an alternative method for his goals to be achieved, namely by enforcing a pact between Hydaelyn and Zodiark.

- Sin Eaters will be loosely tied to the concept of the seven deadly sins.

- The Warrior of Darkness will wield the power of the dark but will not necessarily engage in acts of brutality. It will instead be a matter of proving that light is not always good and dark is not always bad. Both are necessary for life as we know it to persist.

- The story will continue to highlight that various individuals and factions are much more morally complex than initially assumed.

- Varis will be revealed to be occasionally possessed by Solus as part of the plan to sow chaos within Garlemald. He is completely unaware of it happening and will either be freed or sacrifice himself in tragic circumstances. His story may have loose similarities to Golbez moving forward.

- The First will highlight that the only way for those on the Source to survive is to put aside their differences and find common ground. As a result, both Garlemald and Eorzea alike will need to engage in some serious diplomacy and self reflection.

- The sixth zone will be a light tainted wasteland located behind the large wall shown in artwork that depicts the region Eulmore is a part of.

- Those living within Eulmore will have forged a pact with the Sin Eaters in exchange for a shaky alliance of convenience.

- Solus will be the main antagonist of the expansion and will have no loyalties to anybody but himself. He will inflict something nasty upon Garlemald but will fail to account for the survivors banding together, seeking outside aid and striking back.

- Solus himself may or may not be dealt with at some point during Shadowbringers, yet his actions will play a part in setting up 6.0 as an Ilsabard focused expansion.

My biggest 'out there' theory:

- Norvrandt will somehow be 'grafted' to the Source. The New Year's poem makes me suspect it to be a slim possibility.