It's sure hard to think clearly in the morning, yep twice as much
Thank you for the information about weight, suspension and that the down should go to the inner layer. With the zipper I was thinking the same thing as WV. If you would make the outer layer large enough so it wouldn't ruin the loft of the inner one. With the zipper, the layers would be always at the same distance of each other. You wouldn't have to fiddle as much with the suspension. How about this with the zippers, hammock, down layer, air gap between layers(maybe 1-2in?) and primaloft layer. If you had all of the sides of the UQs firmly pressed again each other and wouldn't the air gap give you more insulation? (in a perfect world this would work... probably...).
For suspension I am thinking about triangle thingies which go over my hammocks ridgeline maybe you could add two triangle pieces to the middle of the ridgeline (and have something to keep them from sliding). The suspension would support the outer layer, is the zipper enought to support the inner?
I added a professionally made illustration about this. The pink blob is the uq, yellow triangles well triangle thingies (four of them). Orange line some line to hold all of the triangle thingies in place. Pink lines are shock cord. Material wise cuben would be light
This sounds so heavy.