I look at it this way. The "must save" possessions that most people board with (wallet, phone, papers, meds, laptop) would usually fit into a laptop bag or decent sized purse. That could be stowed under the seat, and to be honest, something that size and weight really isn't going to impede the evacuation much.
The real problem is these 50 pound overstuffed suitcases that just barely fit into the overhead to begin with - probably packed with a week's worth of clothes and whatever other stuff the owners could get into them. If you get those suitcases into the hold, you've solved most of the problem. Now, yes, there's still going to be a few people with expensive camera equipment or musical instruments or the like, but that's more likely to be the exception.
How do you get the bulky suitcases into the hold? Maybe offer a ticket discount if you check any bags over a certain size, rather than charging extra for them. I still think the airlines created much of this problem when they got greedy and started charging a fortune for checked bags.