I guess the advantage of having an HDPE roadbook is only because it is cheaper. The flexibility is lost due to the geometry (an open box). So it will not give room (or not give as much as you would think) in order to try something like that. I would prefer the frame to take the blow and give away in case of an accident. Making the equipment itself flexible will not help as much.
A roadbook from composite materials will be lighter, you dont have the Aluminium welds as well but all in all it may be more expensive. touratech did not sell but then again Touratech did not sell well even with its Aluminium unit
The other thing that needs to be considered is that, let's say in Paul's design (because we have seen how it works, no offence Paul) say that the tower goes forward. That means that the fairing will most probable break and then the tower itself will be exposed. I am with safety here and I would prefer 1oo% to buy new equipment than to imprint my chest onto the roadbook but it needs some calculations so it does not break with blows that may not hurt you in the first place