Once upon a time, I was told on Trollmegle by a particularly angry Karezi fan that the proof that Karkat and Terezi were soulmates lay in that their trolltags are made of the same two letters.
If we are to assume that it is the case, the endgame pairings in Homestuck would be as follows.
CGGC (Karkat/Terezi)
TCCT (Gamzee/Equius)
TGGT (Dave/John, using John's original chumhandle because otherwise he ruins the system.)
ATTA (Tavros/Sollux)
CAAC (Eridan/Nepeta)
AGGA (Vriska/Kanaya)
This leaves AA, Aradia, CC, Feferi, TT, Rose, and GG, Jade, separate. As all of the above pairings are troll/troll or human/human, we can follow this pattern