I got a few more questions answered about matchmaking this last season that reinforces the knowledge of some known rules. Matchmaking can put players of a greater displayed skill level variance to their teammates than the posted grouping restrictions (i.e. a Platinum and a Masters ranked player in the same game), but you cannot group up with other players if your skill ratings exceed the posted SR limits (1000 for Diamond and lower, 500 Masters, 350 Grand Masters). This is in contrary to the statement in the Season 8 Competitive Play News Blog Post.
Secondly the 40% minimum chance of winning a match is still a rule in Competitive Play matchmaking. I didn’t get details on this, but I assume that calculation is based on the following formula:
X = 100 * (A / (A + B)
X = Estimated Win Percentage of Team A
A = Average MMR of Team A
B = Average MMR of Team B