Multiplauyer KOTH (M-KOTH ?) idea sounds great to me.
IMHO the main question now is how to adopt the KOTH format (bottom-middle-top) to the M-KOTH.
Here is one possibility (surely not the best solution, but still better than nothing

)
Hill is formed of 3 levels: bottom, middle, top (and the place for king of course).
Bottom level: 10 players. First 5 losers stay in the bottom level, the other 5 move up to the middle.
Middle level: 10 players. First 7 losers move down to the bottom level, the other 3 move up to the top.
Top level: 9-10 players (9 players if there is no king, otherwise 10). First 9 losers move down to the bottom level, the winner becomes the king.
Seems rather simple. No I tried to calculate how many Groups need to finish the games in order to elect the first king...
2 Groups in the bottom gives 1 group in the middle.
3 Groups in the middle gives 1 group in the top.
1 group in the top gives the king.
So we need 10 Groups to finish their games to elect the first king. That's pretty much and it will take a long time.
Maybe decreasing the number of players in the Groups could help?