On an unrelated note, I was recently watching a DS9 episode where they’re in the Mirror Universe aboard Terok Nor, the Cardassian name for DS9. In the Mirror Universe the station is still a Cardassian station, because the Federation doesn’t exist. But there’s this one point where Evil Kira talks to the computer, and the computer voice still sounds like Lwaxana Troi, instead of like, some Cardassian voice. That irritated me so much I actually wrote this post about it.
Well, Majel Barrett did play three live-action roles in the franchise, not mention the various characters she voiced in TAS, so this isn’t the biggest implausibility the Mirror Universe has to offer.