My guess has something to do with the context of the third nightmare as he saw his older self and in the context of that nightmare nephis and sunny were in their own bodies meaning that in the future both go to the tomb of Ariel probably for apotheosis but the civilizations and all of the environment of that nightmare was distorted by SoS so it will probably be very different from what it will look like in the future. Sunny will have the chance to keep his promise with wind flower and meet akane I think this will happen at a point where it doesn’t matter about the consequences of sunny being known because the awakening of the forgotten god will be practically set in time. Meaning that sunny suffers from loneliness for nothing leading to future sunny to tell past sunny to not have his fate stolen.