Over the years, passengers have been getting larger and seat pitch ever smaller. But according to Sukhoi, the Superjet 100 has around 32" seat pitch in 2+3 for most economy class seating - which is far more generous than the absurdly cramped 180 seat 3+3 configuration Lufthansa use in the A320neo.
So it's not just passengers grabbing luggage which could impede an evacuation, it's the difficulty some would have in even trying to get out of cramped seats in the first place.
If more airlines reduce cabin baggage allowance, there is every chance that many airports won't be able to cope with additional baggage loading and unloading. More luggage will get lost or damaged - which is probably why may passengers now try to avoid checking in the luggage. On short trips with Lufthansa, I now use a 'cabin trolley' which I bought from them as it is advertised as being compliant with their cabin baggage allowances; I always check that it is within their 8 kg allowance. It goes in the overhead locker, whereas my passport, tickets, phone and car keys remain in my pockets.
But do other passengers ensure that they comply with the rules? Absolutely not, going by the number of 'aeroplane mountaineers' one sees struggling down the aisles with their bergens.
I hope that Vladimir Putin will decorate the brave cabin attendant who did such sterling work with a suitable award.