Mm not sure about that one. If I were guessing I'd say that mirror emperor is either Georgiou or Cornwell.
Or Stamets. :) This theory is now popular too.
Discovery started out very, very bad. Let's see whether it improves and explains at some point, why they mistook some refugees from the planet of the apes for Klingons.
If I remember correctly, they promised to explain everything. I'm more interested in their explanation of mushroom drive because in original series there was mentioning that Klingons. After all, they was redesigned one time and there was an explanation of this: https://www.youtube.com/watch?v=z0xqaLLydlc
Or here: http://memory-alpha.wikia.com/wiki/Klingon_augment_virus
Also, there is a theory, that Klingons we see on DIS is just some "old" Klingons yet unaffected by recent genetic changes. After all, this is happening after ENT, but before TOS. Maybe before ENT there was also something like that.
However, there is something I really don't like: the super-advance plastic surgery to change species. I find it extremely stupid and I was hoping I'd never have to see it again. Oh well, at least it was not a holodeck malfunction. But if they are going that route, at least the story is interesting enough. It reminded me of the sleeper Cylons in Battlestar Galactica. And of course, the idea is very similar to one DS9 episode (with a totally different resolution).
Actually, Klingon disguised as human is canon and right from TOS:
The thing is, this is basically beat for beat the plot of “The Trouble with Tribbles,” albeit with a great deal fewer darkly lit interiors and savage beatings. In that episode, a Klingon agent named Arne Darvin masquerades as a human to infiltrate a Federation post, where he attempts to poison grain meant for a planet with disputed Federation-Klingon ownership. Darvin is only outed because the innocuous, fluffy tribbles have a particular hatred of Klingons, and tend to freak out in their presence, which leads Kirk to discover his identity and save the day.