Time travel can be a difficult theme to handle as it can easily be done poorly.

World of Warcraft handled it so poorly in Cataclym and then based an entire expansion on it just to bring back old characters that were killed off. "Hey, how do we defeat this powerful dragon aspect that's infused with the blood of the Old Gods? I know, lets go back in time and take the item that has made him so powerful and use it against him in the present!" I preferred it when we were simply trying to stop some mysterious dragons from changing the past in order to destroy existence.

I much prefer how its done in FF14. Even though we don't know what we're doing, we're actually doing exactly what we're supposed to to complete the timeline.

I mean, they could introduce Ultimecia and have a time travel based storyline, but it needs to be done well. And as much as I love the little guy as Vivi was my favourite character in FF9, I don't think bringing back Gigi would be a good idea. People are already complaining about having to do Hildibrand for the relic, they'd be fuming if they needed to do it for the MSQ.