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Alright, I'm gonna play this out how I think it could work for this. It sucks to only advance one player out of a pool, but if you want to have this even remotely manageable timewise, you have to do it. If you want to advance 2 from each pool, it's feasible, but the championship bracket will take twice as long if you do double elimination.
We're going to make this play out a certain way just to show how it could work.
Pool A:
#1 seed
Random
Random
Random
Pool B:
#2 seed
3 randoms
Pool C:
#3 seed
3 randoms
Pool D:
#4 seed
3 randoms
Pool E:
#5 seed
3 randoms
Within each pool, each player will play 2 games (not best of 3, just two games) against each other player in his pool, one level picked by each player. (We can still do advanced slob picks and stuff like that) After the round robin, each player will have played 6 games.
Lets say here are the results: Pool X, player advancing, record in pool
Pool A: #1 seed, 6-0 (call him player Q)
Pool B: #2 seed, 5-1 (call him player R)
Pool C: #3 seed, 6-0 (" " " S)
Pool D: #4 seed, 5-1(" " " T
Pool E: Random player, 6-0 (Player U)
After this, we would reseed based upon original seeds and results.
#1: Q (6-0, pool A)
#2: S (6-0, pool C)
#3: U (6-0, pool E)
#4: R (5-1, pool B)
#5: T (5-1, pool D)
R and T get the lowest seeds because they had the worst records in the Pool play, with R getting the 4 because he was higher seeded earlier. Q, S, and U are placed for the same reasons.
From there, it's a simple double elimination bracket.
Now, as far as only one team advanced from each pool, we could easily do this with 2 teams getting out of each pool, it's just going to make seeding much much more complicated. We would do the same as I did above, except with several more players and records. As far as making the championship bracket slightly shorter with the 2 players from each pool format, we could do only double elimination for the last 8 remaining. So depending on the number of pools, we have a series of play in games to get to the final 8, and then the final 8 do a normal tournament.
As for seeding before the pools, I would suggest just breaking up the top X teams in order to make the top seeds and put them in their respective pools.
As far as time goes, if we have 8 pools, and 8 set ups. We'll assume each game takes 4 minutes.
Each pool has 12 games. (each player plays 6 games, count them individually if you don't believe me) With 12 games, it should theoretically take only ~50 minutes to do pools. To play safe, we would have to assume it takes an hour. We would then take a half hour or so to do seeding, then play it out. The singles could take as little as 3 hours overall played with this format. If the people running the tournament are on the ball, we can easily finish both singles and doubles in plenty of time.