I'm a little confused about your last post given the earlier comment about wanting just one round trip plane flight. You said most recently:
"I would start the AT with the pack in march, skip the snow, do the desert in the winter, skip the heat, then head back to the PCT and go southbound? I feel like I'm still going to be coming back to early to the PCT (middle of june), don't most start middle of July? I'd rather not sit around for a month and lose the fitness from the AT"
Skipping Fuller Ridge, Baden-Powell etc means what --- just skipping them entirely, or coming back to do them later? Given the snow year anticipated, I'm guessing a PCT SOBO will be better started in July this year rather than June (that said, I'm hoping to start a CDT SOBO in early June ... TBD).
I don't think you can "skip the snow" on that AT unless you start later, though it will slow you down. I assume you have experience in snow --- there's no way you can do two trails in the same year and not deal with a fair bit of it one place or another. The snow on the AT will NOT be your biggest snow challenge.
I don't think you should focus on "skipping the heat" --- a PCT SOBO should get you into SoCal late enough in the year that I wouldn't worry about that.
You definitely don't want to sit around for a month. The time it will take you to get from one trail to another, plus whatever time off you allow yourself, will be as much as you want to take off. With a Feb start on the AT, you can potentially finish in June --- if you have a hope of doing two trails in the same year --- and then with some time loss in between start on the PCT sometime in July.
If you're set on flipping back and forth more, by all means, but I think it will be easier and cheaper to do all of the AT and then the PCT. Just recognize you'll go from nice weather in Maine to potentially a whole lot of snow still in northern Washington --- big snow year, best guess is for a late melt out, which makes any PCT SOBO a more difficult challenge this year. That is perhaps the biggest wild card in your plan I think.
You might well end up doing some flipping on the PCT to do large snow-free chunks first. Maybe start north of the Sierras and walk to Canada, then flip down to do the southern ~thousand miles southbound walking from, say, Sonora Pass or something like that. Tough to say for sure at this point.