What is the offside line for the side that hasn't a player in the mono-ruck? That side has no 'hind foot' to set the line.
Is it the hindmost (closest to goal) body part of the opponent or the ball?
If it's the ball then that would be a very good reason not to put a player in the ruck.
I had a chat to a local referee who had seen the changes ahead of time and he had asked the same question.
The answer he got was a bit vague, but it seems that when a player enters the tackle on his feet to form a ruck, a line through the back his hindmost feet is his team's offside line, and the line through the tackle gate on his opponent's side of the tackle is the opponent's ruck offside line, until an opponent joins, then that player's feet mark the offside line
And for those asking if this wording is like the Mitre 10 cup, the answer is no. While they also had one player form a ruck, there was no gate as such. the offside line was the ball, and players could enter from anywhere in a 180° semicircle on their own side of that line. That resulted in a mess, with the only benefit being that players mostly tended to stay on their feet (very upright) to try to either kick the ball through or win it by hooking it back.
In this case, the gate still exists. Team mates of the mono-ruck former will have to join alongside him and from behind him. The first opponet will have to arrive through the gate and subsequent opponents will have to join alongside him or whoever is the hindmost player.
Frankly, I think this "the game is turning into League " bollocks is just OTT scaremongering. I watched all four Super Rugby quarter finals this weekend.
Total numbers of breakdown turnovers across all four matches = 118 (30, 29, 28 and 31 over the four games in that order.)
Of those, the total number of breakdown turnovers from
tackle assists and jacklers arriving and pilfering ball (or winning a PK through the tackled player not releasing) = 85
The numbers of breakdown turnovers from
tacklers getting to their feet and, pilfering ball (or winning a PK through the tackled player not releasing) = 5
I don't think making the tackler go through the gate is going to make the dramatic,
"end of the game as we know it" difference that some are claiming.