It was a fun contest and probably one of the easiest event to bring people together. Judging by the participants, it was definitely a successful contest.
In terms of suggestions, once we get to the last 16 you pretty much know your chances of winning, and it's a battle between a handful only.
In addition to the current form,perhaps you can add different contests, like
- have a winner at the end of the first stage from 32 to 16
- reset the contest from last 16 and have another winner
- guess the final 4 or 8 before the first match
- winner for the longest correct streak
We indeed noticed a small drop in the number of participants at the end of the contest, perhaps because they focused on the fact that they would probably no longer reach the top of the ranking, while each badge won also increased their rewards at the end of the competition.