Like it or not, cabin baggage appears to have been an issue for at least some of the pax which for them turned this accident from survivable to non-survivable. This is an aspect that will be addressed by the accident investigators because they are required to do so by Annex 13.
IMO, the investigation needs to look primarily at why the approach became unstable, why the hard landing led to fuel tank rupture, and why so many pax died.
It is apparent from some of the video evidence that the hull breach from the extrenal fire occurred quite early (+50 secs?) - you can see smoke issuing from the top of the forward doors while there are still people coming down the slides - which means that those at the rear of the aircraft would have rapidly been in an unsurvivable cabin environment. There is also a 6-7 second hiatus in pax flow from the forward right slide which ends with someone carrying a large bag; that delay will have costs lives.
I am strongly of the opinion that central locking for for the overheads is the only way to go. It certainly stands more chance of success than trying to persuade airlines to stop permitting cabin baggage, which is not necessary. Once people learn the overheads will only be released once on stand, they will be less likely to try to retrieve items, and if they try they will soon be moved on. If they are not locked it only takes one person to open them before others follow suit, and that will impede the escape of those behind them, whether from the time delay or from a newly introduced trip hazard. How much more evidence do we need for change, and how many more will have to die before something is done?
Now let's add seat pitch into the mix. The FAA and EASA have refused to rule on seat pitch, the FAA claiming that the low pitches being considered (27"/608cm) would not affect someone's ability to leave their seat quickly. That is worth thinking about as an official position, because even the most cursory examination would show that you reach a physical limit at some point. And what about seating density? All exits are rated for pax flow per 90 seconds, but unless you pay to be in PE or business+ where the pax/metre equation is lowest, you are likely to be up against the limits.