Thoughts on large numbers of players in one chess game

I have recently been working on chess variants with a large number of players. This has proved problematical, for the usual reasons: ganging up and time to play.

Ganging up I have solved with the rule that every player's victory condition is to checkmate the player to THEIR left. This largely removes the advantage of teaming up with other players, since a player must now focus on attacking to the left while defending from the right. This has worked well with 2 (against each other as normal) 3, 4, and 6 - not so well with 5 since I have not yet come up with a pentagonal board variant that would not leave someone at a disadvantage attacking over a gap.

The time is a toughie. With 6 people each taking just 5 minutes a move, you only get to move once every half hour and games take an eternity. My current, as yet untested but attractive, thought, is for every player to WRITE down their move in secret, and when everyone has done so, EXECUTING them in round-robin fashion clockwise from the white player. These moves are all based on the situation at the start of the move, and may not be valid if someone to your right changes the board, but the occasional odd move becomes a part of the game.

Moves should be specified by coordinate even when capturing. That way, a move to "a7" to capture an enemy piece does not become invalid if the piece moves before the capture takes place, it merely mutates into a move to a new space without a capture - or, if another piece interposes itself, the move becomes a capture of the interposing piece and the piece stops short of the objective square. At five minutes per move segment, this lets everyone play once every five minutes. It becomes important to anticipate what your opponent's moves might be to avoid making pointless moves due to changing conditions.