It was very apparent that Supergirl was having troubles when it premiered last fall, and even the crossover event with The Flash might have helped. Still, it was on CBS' chopping block at the end of the spring, and the Season Finale was actually thought to be the Series Finale. Suddenly, the CW network has swept in to make Supergirl its own, and it is possible that she will be joining the same universe as Arrow, The Flash, and DC's Legends of Tomorrow. However, from Supergirl's first episode, it has had a Superman problem, but this will be resolved in Season 2.
According to TV Line, Warner Brothers has revealed that "the iconic character of Superman will first be seen visiting his cousin Kara in National City at the beginning of the series second season". That is right, Superman will finally be fully seen, and there is casting for the iconic role underway.
The first episode of Superman revealed a different kind of origin for Kara (Melisa Benoist) as it is revealed that she was supposed to look out for Kal-El (Superman's Kryptonian name). Unfortunately, Superman's ship arrived on Earth as planned, but Kara's ship was sidetracked due to the Phantom Zone interference. So by the time Kara showed up, Superman was already established as an adult hero, and he actually helps Kara growing up.
From the first episode, when Kara narrates, Superman is shown, but never his face. There have even been episodes where Superman has aided Kara in battle, but he is only seen from a distance. As a viewer, it just felt like an odd choice of direction, but it is actually quite common in comic book films.
For example, in The Dark Knight, Commissioner Gordon is seen as having a family. The audience sees that he has a son and daughter, but the daughter's face is never seen. Any comic fan realized why, as the long-term plan for Commissioner Gordon's daughter Barbara (who eventually became Batgirl) hadn't been written yet. It is obvious that the producers wanted to keep their options open in case they wanted to put Batgirl in The Dark Knight Rises (which they didn't). However, if they did decide to use Batgirl, they could cast any actress (preferably A-list) in that role, rather than having to just cast the same actress, if they had shown her face.
The reason why Superman's face was not show was because it could have turned the Supergirl show into another Superman show. It looks like Superman is going to show up, and will more than likely join the cast. However, that could lead to that leading man become the leading man of the show.
So it is now a big question mark of who will be playing the Man of Steel, just like who will be playing the new James Bond. One name that really should come to mind is Tom Welling, who played young Clark Kent on Smallville. This wouldn't mean that the new Supergirl show takes place in that continuity, as Kara was played by Laura Vandervoort on that darker and more realistic Smallville show. Considering that Dean Cain, who once played Superman on Lois and Clark: The New Adventures of Superman, is Kara's adopted father, that casting just makes sense.