To be frank I wouldn't hold my breath, it honestly seems more likely that mythic would go back to 25 than have them create 10 man again.
While they *could* do it, raid participation hasn't changed much relative to previous xpacs when you factor everything in (like time frame, which a lot of the posters in this thread seem to neglect when looking at the numbers). I don't think blizzard will see this 10 man thing as a problem, and there's been talk about how people who work for blizzard are saying they want to go back to 25 because 20 man is still too constricting for similar reasons that 10 is.
So while I personally don't see a reason mythic *needs* to be one raid size, I also don't see blizzard budging on this.