I opened this topic because I think this never got a proper discussion in these forums. During MK's most recent AMA on Reddit, he answered a question about the true identity of the Night Mother, and turned what everyone thought upside down. Here's his answer:

And this is what Sermon 22 has to say, or at least what most found relevant on Reddit:

There were some discussions on Reddit, some thinking that the Sermon represented Vivec replacing Mephala as the patron of the Morag Tong, and that Mephala created the Dark Brotherhood after this, taking the guise of the Night Mother. This is supported by what happened earlier in the Sermon:

However, most others have thought about the possibility of the Night Mother being truly the God King of Morrowind, Vehk hirself.

Look at this statement by MK:

Some have taken this to mean that Vehk's female aspect has been busy playing the Night Mother.

So, what do you all think?? The two sides seem truly good. It's normal that this concerns me, since I was the guy who asked MK the question in the first place.

Mephala is the Prince of Secrets. Now shush, and continue living in lies...

I absolutely adore how people are taking "my" cracky theory and actually presenting it seriously.

Would be hilarious if it turned out to be true, though. "The BEST thing" indeed.