I have made a single and a double summer quilt using 2.5 oz Climashield XP with nylon shells and have been very happy with them.
I made the double with momentum 0.9oz on the inside and nylon ripstop 1.1oz on the outside. On the single quilt, I used nylon ripstop 1.1oz on both sides.
I like your silk idea. My only concern would be that if the silk gets wet, it will wick water into the insulation and silk stays wet for a while. So, if there is any chance your quilt would to subject to condensation drips or mist or spray from wind blown rain, I would use nylon with a good DWR for the outside and silk only on the inside.
BTW, what weight of silk were you thinking of using?