Warning: Spoilers for The Flash Season 4!
At the conclusion of "Finish Line," the season 3 finale of The Flash, Team Flash's celebration of their defeat of the would-be speed god Savitar - revealed as an evil time remnant of Barry Allen (Grant Gustin) from the future - was short lived. Barry and Iris West (Candice Patton) had only moments to celebrate their impending wedding and future together before the Speed Force attacked Central City, looking for a speedster to replace Savitar (and the escaped Jay Garrick, played by John Wesley Shipp), in its eternal prison. That speedster turned out to be Barry Allen himself. Invited into the afterlife of the Speed Force by a vision of his late mother, Nora, Barry chose to bid farewell to Iris and his Flash family and take his place in the Speed Force. Barry had reached his finish line. His race is over.
Barry's departure doesn't leave Central City or Earth 1 without a Flash. They still have Kid Flash, aka Wally West (Keiynan Lonsdale), who now steps up as the new Fastest Man Alive. It's quite a promotion for the formerly long-lost son of Joe West (Jesse L. Martin), but a position not unfamiliar to fans of The Flash. In the Flashpoint timeline created by Barry earlier in season 3, Wally was The Flash, albeit clad in the familiar yellow and red suit he wears as Kid Flash. As The Flash, Wally was embroiled in a feud with a speedster called the Rival. When the timeline was restored, Wally gained his speed powers and became Barry's sidekick as Kid Flash.
Wally was trained by H.R. Wells (Tom Cavanagh) and exhibited traits suggesting he could use the Speed Force to run even faster than Barry ever had. Wally was a major opponent and target of Savitar, who imprisoned Wally within the Speed Force until Barry rescued him and Jay Garrick volunteered to take Wally's place as the Speed Force's prisoner. In the end, Wally played a major role, alongside Barry, Jay, and the rest of Team Flash, in finally destroying Savitar after his sister Iris' life was ultimately saved. With Barry now one with the Speed Force, Wally has a clear trajectory: he can inherit the mantle of The Flash just as his comic book counterpart did.
For a generation of comic book readers and fans of DC Animation, Wally West is The Flash. When Barry Allen died in 1985's mega-epic Crisis on Infinite Earths that rebooted the DC Universe, his sidekick Wally stepped up and became The Flash. Wally joined the Justice League both in the comics and in the Justice League Unlimited cartoon series, bringing youth, energy and boundless comic relief to the League's world-saving superhero adventures. Many fans were dismayed when Barry Allen was brought back to life in the comics a decade ago, and then resumed the mantle of The Flash when DC Comics rebooted their universe yet again in 2011's "The New 52" initiative. The classic Wally West disappeared in the wake of "The New 52," replaced with an African American Wally who inspired the television series' Wally, but Wally Version 1 returned to the DC Universe last year during the "DC Rebirth" event that continues today. Barry Allen remains The Flash in the comics, but with the concluding events of The CW series' season 3 finale, it looks like The Flash might just run in a different, retro direction.
While it's hard to imagine Grant Gustin will somehow not return for season 4, or even take an extended hiatus from the series he stars in, it's an intriguing scenario to have Keiynan Lonsdale be the star of The Flash as its titular hero, at least for the (very) short term. Playing Wally as a sullen and angry teen initially, Lonsdale has evolved Wally into a charismatic charmer. As Barry, who was once the sprightly counterpart to the brooding Oliver Queen on Arrow, grew increasingly burdened by guilt over the choices he's made as Flash, Wally served as a necessary contrast. Though inexperienced, Wally became much more happy-go-lucky and more eager to enjoy his speedy superheroics than Barry was.
With the series now untethered from Barry's perpetual need for contrition, the prospect of The Flash with Wally at the forefront is an exciting one to consider. Lonsdale as the Scarlett Speedster would inject some new youth and vitality into the series. With Iris and Joe lending support, Team Flash becomes even more of a family affair than it was with Barry, who was adopted into the West family. The dynamic with Cisco and Harrison Wells, on loan from Earth 2, changes considerably with the more cocksure Wally as The Flash. Speaking of Wells, Wally's paramour Jesse Quick (Violett Beane), currently serving as the heroic speedster of Earth 3, would be agog to return to Earth 1 and find Wally as the sole Flash of his world. Wally as The Flash also opens up decades of potential stories from Wally's lengthy run of "Flash" comics, as well as the chance to explore Wally's numerous abilities Barry doesn't have.
The CW's Arrowverse shows tend to happen more or less in real time, which means when The Flash season 4 begins, it will be the fall of 2017 and Barry will have been in the Speed Force for a few months. Wally will have had the entire summer to be The Flash, though his adventures will have taken place off screen. Barry will inevitably return, most likely during the season premiere. But when Barry does return, it would be exciting for him to see red... because Wally has been The Flash all this time and is a runaway success.