Rather a late reply.

I've made two quilts and now use them more often than a sleeping bag unless it's below freezing. I think quilts are easier to use in a hammock since you don't have to worm yourself down into a bag from the top.

One is made with 3.6 ounce Apex insulation. I didn't stabilize the layers through the body of the quilt and it has survived several trips so far. I just sewed it around the perimeter with a stack of insulation, the liner, and outer fabric (both <1 ounce per square yard nylon) . Then turned it inside out, sewed a line of stitching around the perimeter, and finished the top edge with a drawstring tunnel. With clothes I might use it to down to about 40 degrees.

The second is a down filled quilt that I've used down to freezing and at altitude.

down quilt

Both have sewn foot boxes and are sewn closed maybe 18" from the bottom.

The draft stopper flaps sound like a good idea.

I sewed loops of ribbon into the side seams. I run a length of flat 1/4" elastic from side to side (kind of like shoe laces) through the loops with a toggle at the top. The elastic helps keep the sides tucked under me and the quilt snugged around me, minimizing air pockets.

I agree that a bivy bag helps manage the quilt and pad system, and helps to keep drafts out, but I more often sleep in a hammock or tent.

Have Fun,
-Bob