CBR has an interview with Geoff Johns on Final Crisis: Legion of Three Worlds, and hints at certain… flashy elements to the story.
“If people liked Bart Allen, they should probably read the book. XS is in it.”
And while he wouldn’t come right out and say whether or not the five-issue miniseries absolutely, positively marked the return of the speedster formerly known as The Flash, Johns teased, “Obviously, one of the big things in ‘Lightning Saga’ that we still haven’t addressed is the lightning rod and what that’s all about. That will be a central focus of the series.”
An image caption also indicates that XS (Jenni Ognats, Bart’s cousin and Barry’s granddaughter) will appear in Flash: Rebirth. While that’s entirely possible, given the apparent scope of the story — and I think it would be great to have the entire Allen/West clan involved — I have to wonder whether the caption writer was misreading an ambiguous paragraph early in the article, which explained XS’ ties to Barry Allen, then added that “The popular character will be showcased… [in] The Flash: Rebirth.“