I think it would be interesting if one airplane did two things.

1) enforce the limit to the number of bags
2) put everything else into a sizer, and check everything that was too big

I'm betting that would go a long way to making this entire carry on thing work for everybody. As it is now, bags are hardly looked at on many flights.

I'm wondering where spirit is going with this. They want only under the seat sized bags to be free, does that mean that you can put it in the overhead for free if there's space, or will they have coin boxes on the overhead too?