Honestly, this is one of the hanging plotlines I'm most interested in because we just don't know how it's going to go. The mission to revitalize the Empty's aether to eventually make it habitable again has been accomplished, but there are still hanging plot threads the characters don't seem terribly concerned about (the context that led to Eden initiating the Flood, where it came from, and solving the mystery behind Gaia's missing memories).

Gaia shares characteristics with various VIII characters, not just Ultimecia. Like Squall she puts up a standoffish front to hide her insecurities, has inner monologues, and acts recklessly when those she cares for are in danger; like Rinoa she's a spoiled rich girl initially in over her head; like Laguna she relies on a "faerie" for extra power in times of crisis; and like all the SeeD characters (except Irvine) she has amnesia. Ultimecia's influence is noted, though whether it's meant to be particularly significant or not I could not say.

Moving forward? Again, couldn't say. Alls I know is, I'm expecting Griever to make an appearance, and will be super disappointed if we don't fight Ultimecia in some capacity (if only for a face-melting remix of The Extreme from Soken). She might not be a very popular villain antagonist due to her very limited screen time and obtuse motivations, but damn if Ultimecia didn't leave an impression through her sheer power and stubbornness during that limited time she had.