The Flash actor Grant Gustin recently revealed that getting to Crisis on Infinite Earths is still their goal. The first time that the event was teased was during the series premiere in 2014, in which audiences glimpsed the titular headline, "Flash Missing Vanishes In Crisis," written by Iris West-Allen for The Central City Citizen. Aside from the obvious references to other DC superheroes throughout the rest of the newspaper's front page, the headline gave audiences two important pieces of information. One, Iris West eventually marries Barry Allen, and two, the Flash vanishes in a "crisis."
For those that don't know, Crisis on Infinite Earths was the world's first major comic book event. DC Comics published the massive series in 1985 (for their 50th anniversary) and they used the series to unite all corners of the multiverse in an attempt to defeat the Anti-Monitor. In Crisis #8, the Flash attempted to stop the Anti-Monitor from using the antimatter cannon, but in doing so, he ran so fast that he essentially dissipated -- and disappeared into the Speed Force. At that point, Wally West (the pre-New 52 version) became the new Flash.
The comic arc was originally teased in the series premiere, and it has been something that crops up every now and then. In an interview with ComicBook at San Diego Comic-Con 2017 this past weekend, Grant Gustin explained that, although the topic doesn't come up all that often, it's something that they want to eventually get to.
"We don’t really talk about on a yearly basis but it was mentioned early on and that's a goal. Obviously, we’d have to go I think ten years to reach that. So there’s a possibility for sure. It’ll be fun to get there."
The article popped up again during season 3 when Team Flash realized that Iris' name had been removed from the byline, thus indicating that she was, in fact, murdered by Savitar. Of course, that didn't end up happening, but that doesn't mean Barry is safe from the perils that await him. Seeing Crisis on Infinite Earths unfold is definitely something comic book fans would love to see, but as Gustin mentions, The Flash would need to make it to 10 seasons for that to happen.
They have already adapted Flashpoint, and the only other Flash-centric event that can top that one is Crisis on Infinite Earths. However, it's worth noting the actual Flashpoint adaptation only consisted of one episode, and the rest of the season was about dealing with the repercussions (i.e. The Flash's own New 52 timeline). Should the series make it to 10 seasons, then perhaps their Crisis adaptation could be the proper way to end the series, with Wally West then permanently taking over the Flash mantle.
The Flash returns for season 4 on October 10.