Since Day 1 when camping, I've seen people sitting around camp with a sleeping bag wrapped around them. If you can keep it out of the mud, why sit around and be cold? There are the quilt designs that have a head hole for a serape style arrangement. You could use the footbox on a quilt like a hood and wrap the rest around you— might be a little stinky in there :)
As to jackets and bags, I think any sleep system should incorporate wearing as much clothing as possible to use the lightest possible sleeping bag; otherwise, you are just carrying more insulation and not utilizing it fully.
I'm on the fence as to working the sleeping bag in as bivouac insulation. If it is cold and windy weather, it is nice to be able to yank a warm layer out for rest stops or open traverses where you aren't working hard going uphill, but there is cold wind ripping down the mountain.
Like this avalanche chute with the trail cutting across (froze my %^&* off):
