Really interesting thread. I have read through most of it. It's a little on the lengthy side for my ADHD riddled brain.
I have a few thoughts.
Seems like the LiIon setup is working nicely for you, but, a bit pricey and complicated.
I think from a $$$$$ point of view, just going with the biggest deep cycle lead acid battery you could stuff under the hood would have been a better option.
I also think that there is a way to go with LEDs. Perhaps there isn't a way at this time to install them into the OEM housings, but, I think that separate running light type LEDs are a viable option, today. Even if they are not suitable due to beam patterns, perhaps they might be suitable for high beam situations only. You could accomplish this by running the LEDs only during high beam situations and the OEM low beams otherwise. Wiring this should be simple enough. Use the high beam feed for the LEDs. Also use it for a relay cutout to the low beams if they don't already cut out during high beam use.
Of course this option would only make sense if you have extended high beam run times. May I ask you a bit more about your commute? I am in Ellington, Ct, so i am familiar with the area. If your commute is along busy two ways, this idea probably wouldn't fly.