The real way to save lives is to decrease regulations, make starting airlines less expensive, get back to the post deregulation days where there were more airlines and lower fares. More people would fly. Less drive. Lives would be saved at a greater rate that any locking bin or redesigning MCAS would ever save.
Well, the regulations that would enforce ban on oversized luggage in the cabin would just revert the situation back to some reasonable point in time, where people were not allowed to bring 15 kg hard case bag and put in overhead locker. And this does not seem like overkill, because:
1. Airplane has cargo hold, where all luggage should be
2. Airplane cabin is NOT well equipped for large amounts of luggage, even there is no evacuation.
3. I remember flying in 90s. Boardings were so much faster than today, you found your seat, you put your small cabin bag in the overhead bin and sat down. Now I routinely see people WHEELING their bags through the aisle, slowing everyone down and then at their seat they are often unable to put the bag to the overhead bin, often crew members need to help.
4. Stewards and stewardesses are not there to handle luggage, there are airport workers who are employed for that purpose.
Therefore, prevalence of large luggage pieces in the passenger cabin is one of the worst aspects of deregulation and I think, regardless of evacuation issues, the size of cabin luggage should go down to what it was before.
Don't want to pay for checked bag? Well, tough luck, you are not allowed to bring it to the cabin - don't wanna pay for the luggage, don't have the luggage. Simple.