The problem with a rating system for a game like Ponds is breaking down the game into binary sets for rating. For example, in chess, it is you against one opponent. The result is rated in a straightforward manner, since the goal of you and your opponent are "diamtetric opposites" -- you try to checkmate, and so do they.
In rating a pond game, it gets more complicated. When someone falls in on round 1, who did they lose to?
Will every player staying in have defeated this person? With the "faller" have lost to the N-1 who remained?
If so, in a pond of 50 players, the first one to fall out gets saddled with 49 losses.
The winner would also have a huge win count: 50 + 49 + 48 + 47... which would be 50 x 51/2 = 1275 at the end!
For rating purposes, I think it make sense to track two numbers: cumulative players defeated (as show above) and binary trials.
Cut the sections down into binary sets. In the case of a section of 64 players, perform the ratings as follows:
Players 1-32 get just one win against corresponding players from 33-64. So 1 beats 33, gets rated, 2 beats 34, gets rated... 32 beats 64, gets rated.
Players 1-16 get credit for a win against players 17-32.
Players 1-8 get credit for a win against players 9-16.
Players 1-4 get credit for wins against 5-8.
Players 1-2 get credit for a win against 3-4.
Player 1 gets credit for a win against 2.
That way, ratings will "stay close" to what we have come to experience as "normal" for other games on here.
And, pond winners in larger ponds will get more points than smaller ponds, yet those who exit early won't have their ratings totally sublimated.