Could some kind of impact absorbing gels be introduced into the aircraft fuselage, to minimize impact damage on passengers & cargo?
Unfortunately, not to any great advantage.

An airliner travels at several hundred kilometres per hour; even when landing and flying at its slowest (which it does only for a very short time) it will still be travelling at a considerable speed.

At such speeds, any impact in a crash is likely to be characterised by two things (I've left aside fire, to concentrate on the matter of impact alone):


a very significant change in velocity (deceleration)
a release of a great deal of energy


The deceleration of an aircraft in flight that hits something will be tremendous. If you have 30 metres in which to decelerate from (say) 500 km/hr to 0, padding won't make any difference to the bodies being decelerated.

If the padding is resistant enough to prevent an object experiencing such a deceleration from simply continuing on its way and smashing through everything in its path, then the padding may as well be a block of concrete for all the softness it could offer.

On the other hand, if the padding not so hard as to smash the bodies that crash into it into pieces, then they will go straight through it and smash themselves to bits on the first harder thing they encounter.

In fact, at such decelerations, not only is there no middle way between too hard and too soft, any padding aiming for the middle ground would be simultaneously too hard (it would certainly cause catastrophic injuries to the bodies encountering it) and too soft (it wouldn't prevent them smashing into other objects).

Then, an impact of the kind you describe releases a huge amount of energy. The things involved in such impacts aren't so much as damaged as cease to exist. Everything stops being what it was. You might as well wish for padding to protect you when you're on the inside of an exploding bomb.

Perhaps you were referring to lesser impacts that would be survivable with some protection, which is reasonable. Indeed, an aircraft can readily survive turbulence that breaks the bones and heads of passengers not wearing seatbelts.

But in this case, the idea sadly fails as not very practical. 


How much damage would 300 or so exploding gel pods, or airbags, do to passengers? Once again, that's a release of quite a lot of energy. 
How much damage would they prevent, compared to say, just wearing seatbelts?
How much would they interfere with the subsequent evacuation?


They simply wouldn't procure any advantage, or at least, only at the cost of a much greater disadvantage.