My synthetic top quilt is a combination of a Speer Frog Sac and a Wiggy's poncho liner. The Frog Sac goes on top of me, with the bottom closed, and zipped up to my knees. The Wiggy's poncho liner goes on top of that. When it's real cold, I double one corner of the poncho liner under my feet for a makeshift footbox. I put the opposite corner above my head to make a roomy canopy over my face.
I'd like a top quilt that is the right size and shape for use inside a hammock. I'm not sure it needs to be dual purpose. It definitely needs a foot box. I suppose a larger Frog Sac would suit me... call it a Possum Sac, with more insulation that the total of my Frog Sac plus poncho liner, and a marsupial-like foot box.
On the other hand, I do like using a two layer top quilt very much. I just bought goose feather booties for $11, so maybe I don't need anything at all!
"We must, indeed, all hang together or, most assuredly, we shall all hang separately." - Ben Franklin