Supernatural is currently airing its 12th season on The CW, making it one of the longest-running scripted shows at the moment, and it is showing no signs of stopping. The show started airing in 2005 when the network was still The WB, with Smallville still going strong at the time as well. It turns out that there was a Supernatural and Smallville crossover that almost happened and the writers had a pretty great idea for it.
Speaking with Entertainment Weekly, director Jackson Stewart, who used to work on Supernatural, revealed what the writers of the show had in mind for the Supernatural and Smallville crossover. It turns out they would have played on the idea of the "Superman Curse" and would have had Tom Welling playing himself in the episode. Here is what he had to say about it.
"There was a lot of really cool ideas that some of the writers had. They had an episode where they really wanted to do a Superman curse that was about every actor who plays Superman ends up getting killed. So they find out that Tom Welling from Smallville is next and have to save him. I thought that was one of the funniest ideas that I'd heard."
It would have been very meta but also would have suited the Supernatural vibe very well. The problem is that it definitely would have been more of a stretch for those working on Smallville to get behind the crossover. This would seemingly have been a lot like the plot of Scream 3, which saw the return of Ghostface killing the cast members of the fictionalized movie-within-a-movie version of the events of Scream called Stab. As for the "Superman Curse" itself, it is a real thing that comes mostly from actor George Reeves, who died at the age of 45 after being shot under disputed circumstances. Christopher Reeve, who played Superman in the Richard Donner movies, died at the age of 52 as the result of heart attack. He was also paralyzed in a horse riding incident back in 1995 before his death.
Smallville ended its run in 2011, but both shows were airing for several seasons side-by-side, so there was plenty of time for this potential crossover to happen. An idea like this also seems like a good way, and probably the only way, a Supernatural and Smallville crossover could have happened. It also would have presented an interesting opportunity for the show to explore a fictionalized explanation for what actually happened to George Reeves and Christopher Reeve.
Smallville hasn't been extremely consistent popularity wise, but it has been a little mixed in terms of quality over the years. Something like this is something fans now can only dream of, but something they would have likely loved to see. There's no reason they couldn't bring in Tom Welling now to execute this idea, since he did play Superman previously and the idea for the story would still work. Plus, The CW is very open to crossovers at the moment and they have been successful for the network, like the Heroes V Aliens Arrowverse four-show crossover that is currently happening. For now, this remains one of those "what could have been" things for fans to dream and speculate about.