You should be able to specify where a player rotates to ie. the bench, Forward pocket, Ruck etc. and tie that in to their fatigue levels.
So for example I select Max Gawn's position as Ruck. I could then set him to Ruck until 50% fatigue and then he rotates to the Forward Pocket.
He continues to play there until he either gets back to say 25% fatigue and then switches back to the Ruck, or he gets rotated to the bench if he reaches 90% fatigue.
The default would be to rotate to the bench when fatigued but you could get midfielders to rotate to the forward or back flanks, talls to the ruck or forward, wingers into the midfield etc.
This would give players a good variety of options and gameplans so we don't end up with midfielders playing in the ruck or forwards playing in the backline etc.