"Right now I'm pretty sure that Bivy Sacks and Poncho Tarps are what I'm going for. What I'm really interested in knowing is if others believe this to be a viable solution."
It is my opinion that a poncho tarp is a very viable solution. I believe Ryan's initial SUL article is testament to this fact as well.
I started with a Campmor/Equinox Poncho Tarp and Equniox Bivy. After much use, in the cooler months here in the Southeast, I am moving on to a Integral Designs SilPoncho and BMW or Oware Bivy (yet to make the bivy purchase). It's hard to beat the weight savings of (1.) such a light shelter, and (2.) the multiple use savings in weight.
Get lighter with lighter materials, as are available through BMW, spin fabrics. I haven't gone this route for durability's sake, but nonetheless, you could pick up an additional 2-3 Oz.
In the Summer I use a Tarptent Virga (also highly recommended) for the bug protection and DriDucks rainsuit. Perhaps, at a moderate ounce penalty, this could be another consideration. Few shelters are as light as the Tarptents for what you get, and I have not come across any that are as easy to pitch. Furthermore, they just look cool.