Andrew Kreisberg’s mention of “multiple shows” likely refers to Legends of Tomorrow, as neither Arrow nor Supergirl regularly feature characters in touch with the Speed Force.
If one of the Legends finally makes the move to end Reverse Flash for good, Black Flash could visit Legends of Tomorrow to carry him off to the Speed Force.
Former Flash supervillain Reverse Flash has been zipping through history and messing up timelines throughout Season 2 as a member of the Legion of Doom.
Legends of Tomorrow has a speedster of its own nowadays.