The main problem with tying the Ultimate Alchemy to the Ultimate Self is that we basically already know exactly what the Ultimate Alchemy is; it involves hordes of grist being pumped into a little frog to make it into a really, really big frog. Now normally there’s little problem in saying that something in Homestuck means motherfucking BOTH THINGS, but in this case it definitely feels like a link in the chain is missing; if Ghost, Frog, Robot, Fairy means anything at all, there’s some connection between creating a universe and reaching the Ultimate Self that I still haven’t managed to figure out.
Had a think about this, thought of some possible answers, then immediately had a cold shower, so I’m fully aware I’m wandering into that wasteland of tensegrile theorycraft for the sake of theorycraft now. With that being said…
When the kids stepped into their new universe (read: capital F Frog), that was their Problem Sleuth “the world is real” moment, stepping out of the pages of the book and into real life. Which does make sense as a step toward becoming your Ultimate Self; even the most powerful supercomputer (read: Robot) can’t comprehend beyond the bounds of the universe it exists in, or the role it serves in a story. In alchemy (ugh, I know), the vessel the reaction takes place in is always included as one of the most important ingredients, to the point that it was sometimes suggested a special container would be needed to contain any reaction involving the universal solvent, lest the container itself be dissolved.
But does this mean anything unless we can universalise it? When the trolls move from their universe into the humans’ domain, is that also a “stepping up” to a higher dimension of reality?
There is perhaps some merit to the idea that even though Karkat and co. literally “created” Earth, Alternia and the trolls are in fact “fictions” emanating from Earth: to the humans, the Midnight Crew who live on Alternia are fictional characters; Lord English, the man responsible for “authoring” Alternia’s history, is a product of earth; and in becoming the Earth’s zodiac and mythological creators, the trolls did, in a sense, become human creations.
One quirk of this interpretation would be that it implies the more “real” a reality is, or the closer it is to the real world, the fewer dimensions it is made up of. In other words, the dimensions of Mind, Doom, Rage and Blood are somehow less “real” than Space, Time, Breath and Light. Though perhaps this makes more sense than the alternative, if we view fiction as an elaboration on reality, rather than an isolated slice of reality?