In a since-deleted tweet from The Flash production office official account, the title for the Season 4 premiere was revealed a couple of months in advance. On July 3, 2017, @FLASHProdOffice tweeted,
"Ready for our first day of filming Season 4! We get started tomorrow, and it's gonna be epic!"
The tweet was accompanied by a picture of the first episode's production board with the title "The Flash Reborn." TVLine caught the tweet before it was removed. The "FLASHProdOffice" account has itself been deleted, though a Google search shows its remnants, where it was described as "The official Twitter account for #TheFlash Production Office Team. Central City."
Thanks to an earlier interview with Candice Patton, who won Best Supporting TV Actress for her role as Iris West at the Saturn Awards, we know that the premiere comes after a time jump (which on a show full of time-travel antics can be a little confusing on its own) of about six months, where they "still don't have Barry out of the Speed Force." In the Season 3 finale, Barry locked himself in the Speed Force prison designed for Savitar so it wouldn't continue to bleed energy onto Earth, which could be cataclysmic.
The word "Rebirth" means a lot to the DC Comics world. Geoff Johns, now CCO of DC Entertainment, President DC Entertainment and co-head of DC Films, did a "Rebirth" mini-series that restored Hal Jordan as Green Lantern and Barry Allen as the Flash after both had died years before. More recently, after the relaunch known as "New 52" started to falter, with many critical of the dark tone of the DC Universe (they literally killed the concept of Hope in that world when they destroyed the Blue Lanterns and their battery that channeled the emotion, to give you an idea), Johns spearheaded the Rebirth of the entire DC Comics Universe, with every comic restored to a fresh start meant to inspire, as Johns told me at the time, "a sense of hope, legacy, and optimism" that he thinks is central to the characters of DC Comics.
So rather than, as some might, jumping to the idea that The Flash is going to try to adapt a specific storyline or series, this is more likely indicative that they're looking for that sense of hope, legacy and optimism once again. Last season, Barry Allen was literally the villain. Everything he did made things worse, he acted selfishly, and his own personality formed Savitar. Coming out of the Speed Force, however that may happen, and thus being "The Flash Reborn," hopefully we'll see a Barry who re-embraces being a hero and has that signature smile and swagger back.
The Flash returns for Season 4 October 10, 2017.