Here's some scoop on Supergirl from Entertainment Weekly's Natalie Abrams' The Spoiler Room column, which was posted on 4/29/16.
Is there any chance we’ll ever actually see Clark Kent or Superman on Supergirl? — Mahendra
First, the show needs to get renewed for a second season. Then… maybe someday. “It will always be a dream of ours to be able to have Clark or Superman on the show,” EP Andrew Kreisberg tells me. “Hopefully with continued success, that opportunity will one day present itself.”
Link to the full article:Spoiler Room: Scoop on Grey's Anatomy, Agents of S.H.I.E.L.D., Blindspot and more | EW.com