Star Trek: Enterprise nearly had William Shatner on it as his Mirror James Kirk.
Star Trek: Enterprise really found its legs in seasons three and four. The series brought in the Xindi arc and really dove into establishing Star Trek lore at the start of the Federation. Cameos from other Trek cast members were happening all the time with Brent Spiner, Jonathan Frakes, Jeffrey Combs, J.G. Hertzler, and a few others popping up during Enterprise’s run. One of the big names that were supposed to be on the series but weren’t was William Shatner.
As the story goes, Shatner was supposed to reprise his role of Mirror James Kirk from the Original Series episode, Mirror, Mirror. The idea would be that when Mirror Spock beamed Mirror Kirk away at the end of the episode, he would actually change universes and go back in time. This is where Jonathan Archer (Scott Bakula) would confront and would undoubtedly set up an amazing scenario.
That scenario, pitched by Shatner, would see Mirror Kirk and Archer create the Mirror Universe together, with Archer not intending to help. It was by all accounts a great idea.
Rick Berman killed William Shatner’s idea and pitched something much worse
Enterprise executive producer Rick Berman suggested a completely unbelievable idea where William Shatner would play a random ship’s chef who just so happened to look like Captain Kirk. A temporal agent would then use the dopple-chef to fill in for Kirk in the future. This was a bad idea in Ocean’s 12 and it would have been an even worse idea here.
Needless to say, Shatner hated this idea. The idea was then apparently pushed back and before a better suggestion could be agreed upon, Enterprise was canceled, ensuring that there wouldn’t be a fifth season. It’s very possible this could’ve been the season four finale if it had gotten the green light or the mid-season break for season five.
Either way, it was a truly great idea that was wasted by an executive producer. Sounds pretty typical at this point.