Onside kicks are the football definition of all hell breaking loose. Add in the new rule, and it just got worse. And oh yeah, in many places, you have to do it with a 5 man crew (less in sub-varsity games), which means you probably have only two officials, one on each restraining line, who now have to watch each team staying onside, how far the ball travels, who touches it when, and add on top of that, where the first blocks take place, where the ball was at the time of that block, and in some cases, who initiated the block.
Good luck with that. This was a rule change that was looking for a problem to solve, and no one really thought about the mechanics of working it.