The really uber SUL gear lists you see are typically one season, but there is good information to be found in studying them. The season, local climate and the age and metabolism/cold tolerance of the user can make a difference.
Thru-hikers can change their kit as the season and local climate dictates using their drop boxes to fine tune the gear that is needed for the next leg, so you don't have to haul it all at once.
What is "lots of sleeping gear"? I think a 20F bag/quilt and a CCF or self-inflating pad are typical 3-season stuff. Using a bivy is more of a function of what type of shelter you pick. If you can afford a couple bags, you can trade a heavier bag for more water in the desert sections, etc. Lighter bags can (and should) be supplemented with clothing layers to get maximum bang for the weight. In a perfect UL world, you should be wearing everything for sleep at the coldest temps.
If you live in a northern state, this is a good time to do some cool/cold weather testing and find your cold tolerance. Go for walks in different weather, sleep in the yard, etc.
I would draw from a layering system like this (not all at once) for a thru-hike:
Merino wool socks
Silkweight to R1 type long johns to suit expected conditions
Silkweight to Cap3-ish base layer shirts
R1/Power Stretch mid-layer (hoodies are good)
100g type polyfill puffy jacket (or vest if you can hack it).
Rain jacket or poncho
Light fleece beanie or balaclava
If you lean to being cold (and in dry conditions), get out the down.