When Arrow got its hands on Task Force X, fans were excited to see part of DC comics lore on the show. Then the Suicide Squad movie got announced, and Arrow very quickly had to stop using the characters. Fans have long assumed the movie killed Arrow's plans for the team, but apparently the movie was responsible for their appearance in the first place.
Another part of Greg Berlanti's extensive Vulture interview released this week saw the producer discuss how the TV shows can be a proving grounds for the movies and for comics characters to be considered for live-action. According to Berlanti, Task Force X was brought onto the show at Warner Bros.' request, in order to familiarise people with the characters before the movie began:
To what extent are the comics R&D for the TV and movie properties? Does DC Comics president Geoff Johns come to you and say, "Hey, here's something we tried out in a comic. Let's try it here"? Sometimes, or he has other executives mention that to us. They said to us a year and a half before they started developing Suicide Squad, "Will you guys put [a version of] the Suicide Squad in your show? Because we want to have it as a film at some point." It also happened with Geoff when Geoff and Andrew [Kreisberg] and I were creating Flash.They were both really huge fans of Cisco Ramon, [also known as] Vibe, and had written a Vibe comic [in 2013] to try and bring him back. They said, "Could we please have Vibe on the show?"
This is somewhat unexpected, given how much WB/DC has made it clear they want to keep their show and movie universe very separate. But it's interesting that they were only really added as a test run for what ended up being a radically different take on Task Force X.
I guess if a DC character suddenly appears on Arrow, Flash, Supergirl, or Legends of Tomorrow only to just as quickly vanish, you can expect them to get a DC movie in the not so distant future.