I think a few people come close to SUL on the PCT, but in all honesty, it's not really necessary.
First of all, you end up carrying a lot of water in So Cal so even if your packweight is really low, you don't feel it that much. You can shave your water carried from 12lbs to 6lbs with a little effort toward optimized water management. Yeah, I know if you have 6lbs of water on top of only 5lbs of gear that's even better, but after a point, you really don't notice, which leads to the next point...
Secondly, you end up getting so strong it hardly matters anymore. A long hike becomes your life and you become so strong it doesn't penalize you to add extra things to improve your life.
I added soap and shampoo so that when I got anywhere with a shower I could wash up, including any campgrounds on the trail I wasn't planning to stay at. This also meant carrying a few quarters (gasp!).
I added a skirt to wear in town because I learned quickly enough that it really sucks to have nothing at all to wear while your clothes are in the wash. I had to fashion an outfit from my bivy sack and windbreaker before I started carrying a skirt. That's fine if I'm going to sit in the laundromat, but what if I want to do some shopping while my clothes are washing?
The skirt was nice because I could wear it over my pants and keep vicious mosquitoes from biting my knees and butt.
I also added an extra large can of deet. Vicious mosquitoes deserve a complete fogging of my whole body, not a wimpy little smear.
I also added a cotton T-shirt. Cotton works great in summer. It also keeps vicious mosquitoes from biting my shoulders. Cotton t-shirts are easy to find in an emergency, which is how I came to obtain mine. (A mosquito emergency.)
I added a paperback book. When you're alone, having something to read at the end of the day really improves your morale.
I carried a musical instrument. I think if I did it again, I'd carry a different, much heavier musical instrument. Something quieter to help pass the time and make me take longer rests.