Is there such a thing

I'm following this closely.

I would love a 2 OUNCE sleep system!

Hmmmm. Not sure anything will fill the entire bill, but the Nunatak Back Country Blanket could come close. Opens up completely flat like a "traditional" quilt so you could cover two with it. You can also velcro it into a headless sleeping bag. It has small 'loops' at each end that you could use to attach it as an underquilt (I'll actually be trying this out soon on a Warbonnet Blackbird). I just ordered a TiGoat Ptarmigan bivy so I can tell you next week how well it works in that too. I'd also think a JacksRBetter Mt. Washington could do the same thing (just ordered one of those as well so I'll let you know if I think about it or see this thread pop back up after I get everything).

And I'm not sure why a double bivy couldn't work for one as well. I would think you could always just fold parts of the sides under you, or roll them up a bit, if you want to decrease the interior volume. And any two person tent could work for one, why not? Bigger than you need, but, the Rainshadow you own for instance, is only about 2.5 pounds or so. I've got the Cloudburst 2, slightly smaller and lighter than the Rainshadow, easily works for two, but I've used it as a spacious solo tent as well.

spinntwin 12.5oz
double oware bivvy -with net 18.5oz (is there another double bivvy that's lighter?
jacksrbetter or nunatek quilt 22.0oz (biggest reservation is that they are only 48 inches wide at the foot end – for two people on 20" pads, someones gonna get cold feet)
booties and head warmer maybe another 15 or so between 2

Total 60- 70oz shared between 2

extra bug protection maybe?

currently tent 44, bag 21….plus another bag say 25, around 90 between 2.

hmmmm – this would get me all sorts of places! am i missing something?

NF Beeline 30° bag = 22 ounces
NeoAir Small = 9 ounces
WalMart Inflatable Pillow = 6.2 ounces

Total = 37.2 ounces of very comfortable sleep

What are your conditions? I would say that there do exist many 'perfect' sleep systems, but they exist for very specific condition. If you're talking about 3 season perfection, I'd say there exist only adequate sleep systems. In other words, it'll be comfortable in a certain range, and acceptable above and below that.

I know (and understand keenly) that money is a big factor, but I've largely given up on the concept of having all-use pieces in my gear closet. I need a 50 degree quilt, a 32 degree quilt and a 15-20 degree quilt. I sleep hot, venting doesn't work for me.

I have a Neo Air small for spring summer fall, and I need to pick up an BA Insulated Air core for winter.

I like a Poncho tarp for Sierra camping when the rain is hard but short, and predictable, but for trips where the forecast is for constant rain, I'd rather have a separate, fully enclosed shelter. Also for snow camping.

I would have a water resistant bivy for the wetter/cooler trips and a noseeum bug bivy for the warmer.

My cents.

I would say my Nunatak Arc Specialist is the basis for my almost perfect sleep system.
The coldest temps i'll face is probably around -10-12C. I wear suitable clothing with the quilt, depending on the temp. My hooded Skaha and Montbell Down inner pants take me to the coldest end of my range, and i simply wear less as it gets warmer. My choice of mat varies with the temperature too.
My collection of sleeping bags are now loaners.