I have used a garlington a few times with CCF pads and was originally thinking, why not use a driducks poncho and some tyvek bags instead of the garbage bags, then it would breath a little.
While tweaking my latest gear list, I had a brainstorm, er um brain fart ??, no it was a brain storm for a multi use piece of gear.
Occasionally I might end up on the ground under a tarp or in a shelter so the idea was why not MYOG a largish retangular 1.25 oz tyvek Bivy sack, with a small flap of insect mesh. I could use that on the ground under a tarp, or use it to replace the bottom shell and garbage bags of a garlington taco. You could put the space blankets in it still and it should breath to some degree and I was also thinking you could just have a batt of Climashield in a SUL .06 cloth to stuff in it under the space blankets as additional insul. You could carry say 5 oz for 3 season, 7.5 oz for winter etc.
I would think you would want it floppy with more room on the top for ground, and dropped a bit on the bottom for a hammock.