It is no secret that the DC TV Universe (Arrow, The Flash) is an entity completely separated from the currently growing DCEU that will soon see its first live-action confrontation between Batman and Superman and the debuts of the Suicide Squad.
However, the unexpected success of the CW's shows caused the emergence of a growing fan-theory stating that both the DCEU and DCTV Universe are in fact part of a potential multiverse that could lead to a Crisis On Infinite Earths-type of storyline.
During the recent Dawn Of The Justice League Special that aired on The CW, we saw our first look at the full Justice League roster. Among them we got to see the Ezra Miller's version of The Flash, already played on TV by Grant Gustin. Thus, host Kevin Smith revealed that a scene tackling this particular subject was cut from the special:
“We saw Ezra Miller, who’s playing movie Flash. And we had shot for those that follow this sort of thing…you know, I’m a big f***ing Flash fan, huge Flash fan… I’ve been talking about like why are they f***ing… we talked about it on the show… why the f*** would you create a new Flash in the movies, with all apologies to Ezra Miller who’s a great actor, but like you’ve got a Flash audience and Grant is f***ing phenomenal and stuff.”
Smith then added:
“And we did a piece where we talked about, I don’t know how much I’m supposed to say because they cut it out, and I was kind of bummed they cut it out. But the idea of, ‘Hey man, DC is known for nothing if not a multiverse,’ so at which point I was like, ‘Could they f***ing crossover?’ And he was like, ‘Ahhhhh.’ So doors are being left open and stuff like that for… think about this, you can have Ezra Miller be The Flash and you could also have Grant be The Flash, because there’s a multiverse at work.”
DC is particularly famous for its Multiverse, among other things, and seeing it addressed in the movies is totally in the realm of possibilities. It's impossible to know if that segment has been cut just for a timing issue or because it gave away too much.
Of course the multiverse already has been introduced on The Flash TV show, but we are here talking about a much more larger scale. And I imagine that if DC were to write a story involving different Earths, they would already have fully-developed characters that they could use in case of need. I like to think that the DCEU is Earth-0 (Prime) and the DCTV Universe Earth-1.
This is merely speculation at this point and I could be completely nuts but I have the feeling that DC will have to address the multiverse in its movie universe at one point. It is such a considerable part of the DC mythology that they won't be able to ignore it ad infinitum. And when you already have an universe just waiting to be explored you can't dismiss it.