The problem for many tournament freaks is that they want to go home on Sunday at 4 pm latest, and if they include the Friday for games they have maximally 5 short (4-hours) games to evaluate the tourney ranking list. Without Friday only 3. You cannot determine the champion within such a short game time. Or.. one must accept that - with a purely Draw based counting - players with equal points will more frequently occur. Also the concept of the top table must be reconsidered.
I think - and I have made simulations - that 6 games will be enough to determine a champion. The games shouldn't be cropped, means ended before the natural end which is a solo or a draw, so one may count 1 day per game. That's almost a week, which could be shortened a bit by letting start an afternoon game anyway, for early killed or late-comers, so one could play his 6 games within 4 or 5 days. The non-professionals may still arrive on Friday and play 3 games. Any points made within maximally 6 games (or maybe 4 even?) are counted. A solo pays 60 points, a 2-way 30, 3-way 20., 4-way 15, 5 way 12, 6-way 10, and a 7-way is a DNP (did not play) and counts zero.
The professionals will arrive sooner for an entire week. Of course should such a tournament be held on an excellent location, allowing family and friends of the players to spend great holidays at the same time. Like for example in Ischia, Italy. To attract the "real" professionals a prize money should be set. Maybe 10'000 for the winner, and 1'000 for each solo

Anyway.. don't forget that each Diplomacy game is already a tournament by itself, among 7 players.
Jack