Probably start with challenging a flag, and then also allow them to check for other infractions. Hopefully they just do away with holding and pass interference penalties outside of personal fouls. Players will adjust, such a stupid sport to build bodies and talent around arbitrary rules like "did he turn around in time" or "were his hands inside the shoulders". And you can allow pick plays, WR and TE can tackle corners. Maybe add in a couple more offensive advantages like allow multiple guys in motion, or to start from a head-start like in Canadian football, or few guys on the LOS. These arbitrary penalties on PI and holding really do ruin the game.
