The quorum + threshold would be left up to the host with defaults at 3 players and 70% of remaining players. They can then change the value of the quorum to anything between 3 and 40, and the threshold to anything between 50% and 100%. These will all show up in settings.
The quorum is the minimum number of players who could possibly vote
that much be in the game for this feature to be in effect. If the quorum is 3, for example, you need at least 3 active players (not Eliminated) in the game to vote the fourth off the island- so it works all the way down to a game with just 4 players.
In order for the rule to get abused with default settings, you'll need a game of at least 4 players and 3 of them will have to vote to kick out the fourth one. Scale this up to 21 players and you need 14 of them to vote to kick out any one of them. At 40, you'll need 28.
They could agree to just take out the biggest player or take out a player that they don't like for some personal reason, but it's decentralized enough to make that a bit hard to pull off. Worst case, they just took out the player with the highest income in a Practice Game- so no real damage.
The best option, in my humble opinion, is have a pop-up show up for everyone saying "should X be removed?" when someone starts the vote, and people can vote yes or no, and a set ratio (2:1 maybe? or 3:2 can work too) of votes is needed for the player to be removed. This'll prevent tactical removes since several decent people in a game should be able to stop the rotten apple.
A dialog would work- you don't really need to track the "no" votes since it's simpler (as far as implementation goes) to treat non-votes as "no"s (and probably safer too). At that point it's just a version of Vote to Boot which instead forcibly eliminates a player.