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I think it might be like the Tenna prophecy panel ("the lord of screens cleaved red by blade").
That is to say we might see a description of the ending at some point, which will be true regardless, but the specifics of how those words are true can be different, perhaps radically so, if it employs some sort of wordplay. I think this also lines up with the stuff Gerson said about writing in between the lines and reinterpreting stories.
Though, seeing as how the scene apparently came to Toby in a dream, I could also imagine the ending being very surreal. Something along the lines of the characters pointing out that you could modify the game's text to be whatever you want, solving whatever conflicts exist within the setting. But how that wouldn't be "real", and some sort of discussion about what makes something in fiction feel 'valid'.
Chapter 5 spoilers
The fake stats, among other things, in chapter 5 might be foreshadowing this. IMO there was a lot of stuff in that chapter that felt like a fangame or mod. I think that was intentional on Toby's part, due to it being flowery's 'fanfiction' (at least until you get to the castle, then it feels a lot more like a 'normal' deltarune chapter). That could just be a part of the 'nostalgia and clinging to the past' theme of the chapter (its first part is like a remix of chapter 1), but I feel like each dark world has taught us a very specific 'lesson' about how dark worlds work. And I feel like each of these 'lessons' are building up to something.