NPPL Rules - 6.27 Padding in Garments will be limited to elbow, forearm, knee, shin, & hips, provided that the padding has not been modified from the manufacturer’s original form. Any other soft padding in garments is prohibited.
The new NPPL rules address where padding can be located, as well as how many layers of padding you can have (one). One of the big problems is actuall enforcing all the equipment restrictions.
Equipment assessors would help with this. But field refs have to look for things like untucked jerseys. That starts getting into the area of ref training (threadjack alert)
I think there needs to be more penalty if you get caught wearing two sets of armpads, three jerseys and a Barney costume on the field. Right now, you're just told to take it off before the game starts. So wear the extra pads and if you get caught you take it off, if not you get some extra bounce. Change so a player with too many layers is eliminated before the game starts and you might see fewer players doing it.