Tom Welling recently spoke to Buzzfeed about his 10 year-run experience as Clark Kent/Superman on Smallville. He seemed very grateful and proud of the current success of Arrow and The Flash on The CW. Smallville is the show that sowed the seeds for the explosion of superheroes TV shows that we know today.
One particular question didn't make the cut -- a question revolving around whether or not, Welling would be willing to put the costume back on and appear as Superman on CBS's Supergirl:
“There’s people who would like it… there’s people who don’t like it but I will tell you that no one has ever actually asked me to do it. So, I don’t know. It would be kind of odd. I don’t know who he is at that point. He would obviously be Superman.”
This was very a cryptic answer from the actor who don't seems so stoked about the idea of reprise his role. The Man of Steel made some blurry cameos on the show and it is yet to be known if CBS will eventually cast someone as the Last Son of Krypton.
With the success of The Flash and the introduction of the multiverse, some fans theorized and requested that Tom Welling appeared as a Superman from an alternate universe on the CW's show. Tom Welling never accepted to wear the famous costume and it's not sure that he would like to be plunged into this word again.
Possibilities are endless and it is sure that the writers would really like to include Superman one way or another. But with the current creation of the Justice League on the big screen, Warner Bros. is not letting its TV properties a lot of space to experiment with DC characters as much as they would want.