Unfortunately, all carriers have been (and are) loathe to mention problems of any kind. Saying what can happen in an emergency is full of difficulty. Since the type of emergency cannot be known, briefing for multiple options would bring further confusion. Whilst flight deck and cabin crew are trained to hold multiple options in mind at all times - pax cannot.
Following the 'Tombstone Imperative' (book by Andrew Weir) nothing will change unless people die. That is, if lots of people die and it can be attributed to hand luggage being the cause. Otherwise: Nothing.
The UK CAA is, understandably, covering their backsides against the next prang and photos of pax holding luggage on the chute.