I am certain the removal of wood or any other material that rots from the construction has to be a good thing, and if it presents a weight saving or improved structural strength also that's even better, But the problem with caravans is not so much the materials used, but the way they are put together. There are examples of older caravans where water ingress has not been a problem, so the traditional materials are still structurally sound. The problems invariably arise because the jointing systems used are not correctly assembled and they allow water in.
With the new systems on offer from all three major manufacturers, there is little doubt about the water resistance of the panels, but its the joints that are still the big unknown. How will they stand up to the rigours of the UK roads and weather.
So until the new systems have seen 5 or more years of real caravanning, their reliability in terms of resistance to water ingress and body movement when towing remains to be seen.
Bailey and Elddis have a few years lead over Swift, so we will begin to see if their systems are better than the traditional methods in a couple of years or so.
I sincerely hope they are vastly superior, as they have had 20 to 30 years using customers as guinea pigs, to understand the problems and design reliability into their construction methods.
I'm still very sceptical as until they manage to de skill the construction process completely so literally the village idiot cannot assemble it incorrectly, then we are still left in the hands of a work force whose motivation is units through the door rather than taking a pride in what they do with bonuses paid on maintenance of quality (e.g. right first time) rather than quantity.