I disagree since the second best NA team might be better than the 1st best SA team and vice versa. I think its better to take the upper threshold of both regions and battle it out even if it means sending all NA/SA teams to represent Americas
my guess
masters 1 #1 and #2 from SA and NA compete in playoffs
masters 2 #1,#2,#3 from SA and NA compete in playoffs
champs #1 from each respective regions, last 2 seed are fought between #2-4