Definitely interesting thoughts, to me anyway. I bought some small AP membranes for use in some bookshelves - there ends my experimenting with AP, and that already puts me in a rarefied crowd.
I'm scratching my head trying to think of how it would be possible to build a water resistant membrane (to the degree that the whole splashy underside of the car is exposed - so I'm sure he wants a real weatherproof seal, at least sealed from a weather standpoint) without being at all air resistant?
I could be wrong - I'm just thinking that by the time it's truly weather resistant, it must behave like an AP membrane. No sacrifice of course - you don't really need airspace for those either.
And conversely - if you let up on the weatherproofing a bit so that it won't have any air resistance, then it won't really be weatherproof.
So you and I are really on the same page - I'm wondering where on that spectrum this membrane is going to fall also - probably just depends on the execution, which I'm staying tuned for.
I love this install - if you put that mock-up picture in front of most car audio enthusiasts, they'd laugh and say something like "Can you imagine if that were real and not obviously a photoshop job?"