I see that Grand Trunk has a hammock sleeping bag in the peapod style. It uses Thinsulate (the specific type wasn't identified), 88" x 34" and 2lbs 10oz. $179.95 MSRP.
It's not a bad effort for a company that is on the inexpensive side of the market. I would love to see the cottage makers whip up an UL version. It begs to have a face net like a bivy, which would negate the need for a full bug net in all but the warmest weather.
It still perplexes me that someone doesn't just make and integrated system with hammock and sleeping bag all in one. It just needs to have a removable suspension for easy laundering.