Asgore IS definitely going to be in chapter five or six. My proof? Obviously there is Gerson saying “the field of pink and gold” in his summary of chapter five of the Lord of the Hammer. Then there is the Egg Man saying that “on Sunday, I harvest the wheat”. As chapter five will probably take place on Sunday, then that means the egg room will be in an area with wheat. An area that has a lot of vegetation and is a likely candidate for the Dark World? The Flower King.
Just look at Queen and Tenna’s prophecy panel names. Respectivel,
Because that’s just way too much for one chapter.
You’re proposing two entirely unique dark worlds, likely with different themings, with enough time to get a good showing of the dark worlds, in ONE chapter.
And they’re continuations of a single story and set of ideas, if there were completely different dark worlds that are both supposed to have their own serious storylines it would definitely feel cramped