Back in 2004, William Shatner pitched a Mirror Kirk story to the producers of Star Trek: Enterprise
to celebrate Trek's 700th episode (which eventually became the totally different "In a Mirror, Darkly" two-parter)
Memory Alpha wrote:
According to Judith & Garfield Reeves-Stevens , the episode idea Shatner had pitched would have featured him as "Tiberius", the mirror universe James T. Kirk last seen in " Mirror, Mirror ". Supposedly killed by mirror- Spock in his rise to power, it would have been revealed that the Tantalus field did not disintegrate, but in fact relocated its victims to a penal colony in the prime universe. If this story were to have been filmed, the Enterprise NX-01 would have encountered Tiberius in the 22nd century, who had been deposited there forty years earlier. In an attempt to return to the mirror universe, using the transporter of the Enterprise, Archer and Tiberius end up creating the mirror universe in the first place, as a diverging timeline.