A tangential answer that may at least partially answer it. I happened to come across a very spirited discussion in an aviation video comments section on this topic. It was enlightening and somewhat surprising to hear so many different opinions, and to find out what average, random travelers think about this topic. Which I think could possibly impact what the airlines' policies are on this even though it's a potential safety issue. And it could explain why there isn't a lot of discussion about this from the airlines.
Previously like many I thought it seemed pretty straightforward, and that anyone taking their carry-on or whatever items with them during an evacuation is just a degenerate, unprincipled reprobate who probably should get the book thrown at them. But a surprisingly large percentage felt differently. I almost think it was even a majority. One point made was that it’s not so simple getting your stuff back. Which makes sense when you think it through. They can’t just let people back onto the plane to go back to their seat and get their items. If it was that easy then it would be no problem. Instead it all has to be collected and taken somewhere, and then there is a process of matching people to their items. I have no idea how it’s done but it sounds messy, and it apparently does not necessarily happen the same day. And it seems quite possible that items will be returned to the wrong person based on misidentification, since this is presumably done through a formal written process, similar to a lost luggage scenario where people describe the item that they are claiming. In fact I suspect that the same airline personnel who handle lost luggage and items left on planes manage these situations, since it's basically the same thing.
From the comments it was clear that there was a lot of distrust of the airlines that they would ever get their stuff back. Justified or not that is what many people felt. A recommendation that was made in the video comments, and even here, is that the airlines should make an announcement of some type reassuring passengers about their items if they are left behind. But since I suspect that the actual situation is not pretty they may be reluctant to do so. An interesting separate question that could be asked is how long does it usually take to get your items back and what is the process, and what percentage of people never get their items back.
A real big issue that was brought up repeatedly was medications. Many people said they would be in danger without their medications, and so had to bring it with them, and because of this they had no intention of following whatever rules there might be.
As relates to the question, I would guess that airlines are aware of these opinions within the travelling public, and they are not likely going to be aggressively pursuing people who violate the rules, because it would not be good PR. And they likely don't want to bring additional attention to an evacuation incident. The only time it would ever be an issue that had to be dealt with is in a worst-case scenario where let’s say the last 25 people did not get out in time, and it had been observed that some people had brought their luggage or small bags with them during the evacuation. However even if the evacuation happened to be caught on video and individuals could be identified, I’m not sure that they could prosecute people who had been seen carrying their luggage off the plane, because it would be nearly impossible to prove that they directly contributed to the deaths of the other passengers. Unless there happened to be say a video of a passenger struggling to get their carry-on out of the overhead bin and holding up the passengers behind them who didn’t make it off the plane.
A really good point that came out of the discussion was that medications should be kept separately, perhaps in a small bag, or maybe even worn in a fanny pack or similar. What also seems clear is that any small carry-on items brought onto the plane should contain some type of ID in them, and preferable on them, perhaps using a luggage tag when possible or a sticker, which includes name, phone number and e-mail. This will likely result in getting the items back much quicker, and lessen the chance of them getting sent to the wrong person. This also could help in other situations for example an item that is accidentally left on the plane or in the terminal.
All that being said, this doesn’t change the fact that each person that takes even five seconds to grab an item creates a multiplied delay, which could potentially be catastrophic and result in unnecessary fatalities. But the odds of this situation actually happening are probably in the millions. There is a chance that luggage being brought down the slide could lead to someone being injured, but this would also be rare and again difficult to prosecute.
I suspect that the situation will remain status quo, and that in the end people will do what they want to in that situation, and they will likely not face any repercussions.