A lot of DC characters were teased or introduced already in The Flash. This time, it seems like a Justice Leaguer was mentioned in a deleted scene available on DVD and Blu-Ray.
EW noticed in the pilot, a deleted scene between Barry and Joe hinting directly at Aquaman. This line from Joe is unequivocal:
"Yeah, and last month you disappeared to Amnesty Bay to investigate a man who could talk to fish."
Amnesty Bay being the home-town of the Fisherman, the easter egg seems pretty clear.
However, since this scene has been deleted I don't think we'll see Arthur Curry appear anytime soon in the "Flarrow-verse." But, I confess that a new small screen adaptation of Aquaman would be pretty cool !
The Flash returns October 6th on the CW.