Douglas, I hope you get some good feedback as I'm interested in this as well.
I slept on the ground between two perfectly spaced trees once. It was before I had my quilts. I was using a mummy bag, a Prolite 4 regular pad, and an Equinox bivy to keep the pad under me. To make matters worst the zipper on my bag and the bivy are on opposite sides. I'm sure you can imagine the difficulty of getting situated in a swinging hammock with this setup. I laugh now, but at the time I was driven to the ground in frustration. That setup worked great on the ground but was obviously too heavy. I tied one end of the hammock to a tree, about four feet up, and staked out the other three corners. For that trip, I was experimenting with a home made pack. The bivy was the body of the pack, so the weight of the bivy didn't count toward the weight of my sleep system, according to my accounting.
Ron, at MLD (Mountain Laurel Designs), had a hammock that looked like it might perform equally well on the ground as in the air. It looked like the shape of the hammock would naturally keep the pad under you while in the air. Ron's hammock is similar in shape to a Speer hammock. Maybe Ron will chime in or someone with experience with a Speer hammock can say if the pad stays put. I don't know if Ron had a chance to deliver any of his hammocks or if they will be made in the future.
I think using a pad, rather than an under quilt, is key to achieving the versatility of air and ground use without a lot of weight. In a Hennessy hammock, the pad needs to be secured in some way or it will be on top of you part way through the night. Maybe someone has an ingenious way to do this. The Hennessy Underpad seems inadequate for ground use. One problem with a pad in a hammock is that I feel it needs to be a little wider and longer than normal because it needs to wrap around you. I know Gossamer Gear sells wide pads for this purpose. I don't know if they are long enough? I'm 6'4".