Watched the Winners tonight, 1985 Prelim between Hawks and Dogs.
You never see more than about 8 players on the screen at any time. There are pairs of players everywhere, sometimes two or three pairs form a pack. The play is never allowed to stagnate. If the players don't move it on, the Ump gives a free or pays a dodgy mark. Ball ups are called quickly and there is no time for big numbers to congregate.
The more I think about this the more I think that the overuse of the interchange bench has nothing to do with the congestion. It is really simple. Pay a free kick every time a player is caught holding the ball or throws it away and the congestion will clear itself up.
There won't be any opportunity to go to ground and pull others down or for multiple players to tackle each other. Don't change anything, just police all the rules that are already there correctly.