The coaches will never emphasise the one on one contests. Ever.
When thinking of new rules, we need to consider why coaches have made these changes in the first place. The answer is always to reduce risk and uncontrollable situations:
Players are around the ball so they can more easily shut down the opposition if they win the contest; sure it reduces our own chance of breaking away from the contest and scoring, but that's fine, it's about risk.
Maintain possession instead of kicking to contests: as above. It doesn't matter if that slows us down, we back ourselves to be more methodical in our attack.
Zones instead of one on one? Exactly the same. Coaches love to get their forward line one on one and their defence in a zone. Why? Because it reduces risk of being scored against.
I think this will reduce congestion, but at the cost of more umpire involvement. The beauty of the game is its free flowing nature (contrast with rugby union of NFL with lots of referee related stoppages) and this rule will need to be policed heavily. It'll also result in very crappy tactics, like dropping a man over your 50 line near one boundary to release a player on the other side of the ground whose opponent can't follow him. That'll make it a farce when there are players who can't pursue their opponents. Imagine winning contested possession then stepping over the 50 line and they have to stop tackling you?
Not explicitly. BUT it makes guarding space much more difficult, and now kicking to leading players is much easier. So although it won't fix the congestion around the contest, it will help alleviate the full ground zone that stops teams attacking from half back. The ball will move through the midfield easier, and although there will still be a zone D50, it will be very hard to "build a wall" to hold the ball in your forward line with two less players. They already use all 18 players for that zone, so it isn't like the coaches can sacrifice any more attack to add to this defence.
I like this idea, but I don't think it will have an effect until late in the season when teams are desperate for points (roll the dice to try to sneak in). Otherwise it will benefit teams that go on a rampage against a weak opponent (which already happens randomly now).
The problem again is risk. Coaches would rather guarantee the win by playing dour than increase the chance of losing for a single extra point.
I think the only way to reduce congestion around the ball/stoppages is to do the following:
Call ball ups quicker. I mean really quick. If the ball is getting scragged and knocked and no one can get a clean possesstion: just blow the whistle before it gets locked in. The idea is that you never want the ball locked in or under a pack in a way that takes 3-10 seconds to get it back to the umpire.
Scrap the nominated ruckman, and don't wait for the ruckman either. Umpire just blows whistle (much more regularly as above), runs in, grabs the ball and throws it straight up, regardless of who is there.
These two umpiring style changes alone will probably fix it: quick ball ups followed by 3rd man up will result in more clearances. If coaches can no longer control risk by creating congestion because clearances are faster and easier, coaches will need to control risk by keeping players out of congestion to defend.
At the moment, coaches would rather wrap the ball up for a set play (low, controlled risk) than hack the ball out of a pack and risk turning it over on the rebound (high, uncontrolled risk). So switch this up through umpiring: pay free kicks around the close contest more often. Pay holding the ball 20 times per game instead of 4. Pay it when someone takes possession at a stoppage and gets wrapped up. Giving an opponent a set play (free kick) at a contest is VERY bad for risk management. So suddenly the lower risk option will be to boot the ball out of congestion, even if it is to a 50/50 contest.
Similarly, pay holding the man for the "3rd man in" to a tackle. Why should you be able to tackle the tackler? It's against the rules and creates congestion. Just pay it, then we'll either have the ball spill lose or a free kick, reducing the number of times the "ball is wrapped up".