Bilojax, Hi and welcome.
You raise very good questions.
I am no expert on airplanes, so my comments are just guesses.

There is a high likelihood that some of the hypothermia cases would have been fatalities if the rescue had not been as fast as it was.
That the rescue boats were available so quickly is largely due to pure luck in where the crash was.
Another point was that the plane had all the external vents sealed to slow the rate it was sinking at.
While this certainly helped if they had been forced to wait a few hours it likely would not have prevented some people from freezing to death.

I don't know about nonslip surfaces on the wings. It might not be possible over much of the wing, but near the exit points would certainly make sense.

I wonder about the raft deployment a lot too.
Getting them out of the water and out of the wind in a raft, huddled together for warmth, instead of standing on the wing should have helped

I was wondering a bit about the inflatable exit ramps themselves.
Maybe they could be made to float enough to keep people out of the water, like the rafts do.

Most people who have never been dunked into freezing water grossly overestimate their ability to swim or even to haul themselves out. Cold water chills you about 25 times as fast as air does.
It saps your strength to the point that at one minute most people are usually too cold to pull themselves out of the water. At 2 minutes the vast majority of people have stopped swimming and are starting to sink, their limbs are to cold to move.

A life jacket might keep your head above water.


An idea about the passenger's clothing.
Obviously most of them were dressed for the airport lounge, the airplane ride and the taxi ride from the airport when they landed, not for standing around waiting to be taken off an airplane wing.
They were certainly not dressed for cold water immersion.

Chris's comment about his survival suit was not a bad one. I thought he was joking at first, but after thinking about it a decent suit of Harris Tweed wool would have been a vast improvement over what most of the passengers were wearing.
I bet even a pair of long underwear would have been a vast improvement in most cases.

I think the investigation report on this one should be a very interesting read, both for what went right, and for what went wrong.
Thanks for bringing it back onto topic.
It is very easy to get distracted.