Hmm, since yesterday I've been thinking; Geno's inclusion could play a role reveal-wise for Sora, and in addition to that, the inclusion of both characters would wrap up what I've come to think of as the "square" allegory. If those two were to make it into Ultimate, Square Enix would have
four characters in the roster (the four corners of the
square). Each character would also represent a different era or circumstance of the company as well.
Cloud: Final Fantasy VII; originated back when the company was known as Squaresoft and entered into the next console generation.
Hero: Dragon Quest (III, IV, VIII, XI); spanning through Enix, and afterwards into Square Enix.
Geno: Super Mario RPG; going back in time when again the company was Squaresoft and ventured into this unique project alongside Nintendo.
Sora: Kingdom Hearts; perhaps Square Enix's modern magnum opus as it collaborated alongside Disney for this unique project.
As for why would Geno's inclusion could work reveal-wise for Sora; although one character is tied to dreams, stars, and working for a higher authority, and the other is linked to the hearts of many worlds, Geno would be in a way like the messenger appointed by the higher authority (Square Enix) to fulfill a dream (Sora's inclusion). For this to happen however, the messenger must be present in its true form (fighter).
This is all speculation, reaching, conspiracy theory, call it what you will but, it's something that was doing the rounds in my head since yesterday.