Yeah, I feel like up to that point in the story everything will be mostly the same as in SM. My money is on the twist happening once Solgaleo/Lunala is summoned and Necrozma pops outta nowhere to steal their light or whatever.The website, to me, implies that the climax still has Lusamine force Cosmog to Cosmoem and that we still do the flute expedition to "awaken" it from there.