The other thing officially stated was "You have our commitment we will be releasing Shadowlands this fall, even if we end up shipping it from our homes". This was stated in the beta reveal video early in July,
https://www.twitch.tv/videos/673613421?t=0h17m5s you can see that here.
Fall to clarify is between September 22nd and December 21st.
I also agree with your comment regarding corruption max resistance - something Blizzard will most likely allow players to play about with for a period of time before removing it. I would imagine this period of time to be about a month.
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The brawl points to a Monday. Expansions historically release in the evening of Tuesdays (Midnight Wednesday in Europe). Yes, this is more than likely not necessarily a pure random number, but a number far enough in the distance it doesn't cause issues before things have been decided, such as a Brawl rotation. Even if the brawl wasn't indicative of a release date, but instead the start of a season of some sorts, again, it's still a Monday.