[SPOILERS for those not caught up on The Flash ahead.]
Production is officially underway on The Flash's fourth season, with the Arrowverse TV show's season 4 premiere episode now confirmed to be titled 'The Flash Reborn'. In the context of the series, the season 4 premiere title makes sense enough and presumably refers to Barry Allen's (Grant Gustin) return from the Speed Force - the place that he wound up (willingly) trapped at the end of The Flash season 3 finale, following his defeat of Savitar aka. "Evil Future Barry".
Iris West herself, Candice Patton has confirmed that the Scarlet Speedster is still trapped in the Speed Force when season 4 begins - meaning, Barry has been in the Speed Force for upwards of six months, by that point. The sheer amount of time that Barry has spent in that strange and mysterious realm will no doubt have impacted him psychologically, at the start of season 4. As such, 'The Flash Reborn' may set Barry on the path to a slow-but-gradual recovery, perhaps somewhat reminiscent of what Agent Dale Cooper has been going through after his escape from the Black Lodge on Twin Peaks: The Return (though one suspects that Barry will be a tad less catatonic, by comparison).
As part of the announcement that The Flash season 4 will be promoted at San Diego Comic-Con later this month, The CW released an official plot synopsis for 'The Flash Reborn' - one that reveals that "With The Fastest Man Alive now trapped inside an extra-dimensional energy, and unknown dangers lurking in the shadows, it will be up to Team Flash to free Barry from his own personal Hell." The official Twitter account for The Flash production office has confirmed that filming is now underway for season 4 (UPDATE: Said link has been deleted, but you can check out the original photo below), but has otherwise offered no clues as to how, exactly, Team Flash will go about freeing Barry from the Speed Force.
The question of what state Barry will be in after his return from the Speed Force, is but one of several surrounding The Flash, following the events of the season 3 finale. In addition to the matter of whether or not Barry and Iris will indeed tie the knot in season 4, the next step in Wally West's (Keiynan Lonsdale) ongoing evolution as Kid Flash will likewise be revealed. Similarly, now that Caitlin Snow (Danielle Panabaker) has fully transformed into Killer Frost on Earth-one, it remains to be seen whether she will serve as an ally (or a sometimes-ally, anyway) to Team Flash and/or if she will ever return to her "human" state as Caitlin. (Not to mention, where does Caitlin's would-be lover - Tom Felton's Julian Albert - fit into all this?)
'The Flash Reborn' will no doubt touch on most of these plot threads, at the same that it brings Barry back into the fold and possibly introduces (or, at least, alludes to) the main villain of season 4. These personal character issues should serve as the crux for The Flash season 4's first half in particular, before the central antagonist of the season properly rears their head. With the next major Arrowverse crossover aiming to heighten the emotional stakes for the shared TV universe in general, it sounds like Team Flash won't be the only superheroes with "personal matters" to deal with, this next season.
The Flash returns to The CW on Tuesday, October 10th.
Source: The Flash Office