I haven't had the chance (and probably won't for a good while) to fully dive into this as potential theory evidence in support of Kriselle!Knight but it cannot be understated the amount of parallels that are parallelling with Weird Route Kris & Noelle, and Homestuck's Gamzee & Equius. (Homestuck spoilers ahead obviously, PROCEED at your own risk haha)
NOW BEFORE YOU DOUBT THE VISION I'm not saying these characters are similar in personality or anything, their respective Venn diagrams would have a very VERY small middle. But Kris (albeit through the player/soul's intervention) stringing along Noelle into a "stronger" person who is willing to harm others for her own gain, it's very reminiscent of Gamzee stringing along Equius after reincarnating him into a broader scheme that leads to the eventual formation of Lil' Cal and subsequently Lord English through fusion shenanigans. The closest equivalent in the Undertale/Deltarune universe we've seen to fusion shenanigans is Undertale's amalgamates, but there's enough credibility to the concept that the knight could possibly be some sort of amalgam, just not the exact same thing as an amalgamate given the circumstances to which the amalgamates were created.
And like if you let me, and I found the time, I could go on about potential connections and shit. Kris's neutral status in the battle between the Knight and the Fun Gang; their rage being directed outward to the soul/player regardless of route, ala Gamzee enraging others (including some readers) through his actions; Noelle saying Kris "makes her stronger" and the whole thing with Equius wanting to be STRONG; her Weird Route counterpart fitting Heir(ess) of Void criteria (even if you abort the Weird Route at the lake, she takes autonomy away from the player out of nowhere, making one incapable of choosing to fully abort at first, and still pulling Kris out of bounds, or into what's supposed to be nothingness, in the process); the emphasized significance of save files and timeline jumping/resetting in Undertale that very likely may become relevant to Deltarune when all is said and done, and how timeline/timeloop shenanigans are a crucial element to Homestuck's story; Toby Fox's numerous references and allusions to Homestuck littered throughout the game, some more explicit than others, and his post mentioning that he's had direct communications with Andrew Hussie during the development process of Deltarune; all of this leads me to believe that on top of like actual textual evidence for the theory within Deltarune, there's potential for Kriselle!Knight to be an external parallel to the eventual creation of Lil' Cal and Lord English in Homestuck.