About penalty goals? Why would that be interesting? I'd happily get rid of penalty goals and replace them with a scrum, except where only the defending team has to include any players. Hear me out.
Those defensive players line up in three lots of two, with a front marker and a back marker, right in front of the player taking the tap. When he taps the ball, the back marker has to leapfrog over the front marker before any of them are allowed to make a tackle. Just think how much space this will create in the defensive line!
Also, the front marker can't crouch too low. He's not allowed to make it easy for the bloke jumping over him. The bend in the knees can't be less than 90 degrees and his hands can't touch the ground. Also, the attacking team isn't allowed to interfere with the leapfroggers or they get penalised for obstruction.