I tried another option, the Black Diamond Tripod bivy, which is really a hybrid of tent and bivy and I didn't care for it. Weight and complexity were equal to a tent and it was expensive, even a used one. There was still no room for gear, the wet-entry/exit issue, and cooking was the same if not worse.
I've considered trying a bivy with an umbrella, giving a little protection for cooking and popping your head out. It is only weight-effective if used as an umbrella for the rest of the trip. Something like one of the pop-up beach sun shelters would be cool– no pitching and still in the "throw it on the ground and climb in" vein.
Either would still meet/exceed a tarp for weight. I set my Gatewood Cape as the benchmark for my shelter choices: 360 degree protection, plus rain gear and pack protection for 11 ounces. No poncho tarp/bivy combo can match it for weight, cost or comfort. It does require space, sticks, strings and stakes.
IMHO, bivys are for emergency use. I carry an AMK rig for day hiking "what if I get caught out for a night" backup.