I've abandoned the idea of a poncho-tarp + bivy, Limited upside (no weight/pack size reduction when stakes and poles are accounted for) and several annoying features: (1) requires 8 stakes + guy lines to pitch the tarp, which takes quite a bit of time and a surprisingly large footprint; (2) minimal protection in windy+rainy conditions. I've "backyard tested" in lousy weather and my down bag was quite damp (albeit not soaked) at the foot. Solvable with an umbrella or some other protection, but annoying nonetheless. (3) Guy lines should be (dis)connected every day. Takes time and makes them more prone to being lost (I've lost two when setting/breaking camp in the dark).

Opted for a one-person free-standing tent. Similar weight, smaller footprint, faster set up, better protection against the elements. Will eventually update.