Versatile 3 season pad combo to 15F. Could this be the answere?

I think a neoair xtherm at 15oz, R5.7 would be lighter, warmer, more simple, easier to pack.

I agree, for the cold end of the spectrum it is warmer and lighter but is overkill during warmer months, not being as versatile. Plus the taper on the neoair x-therm and x-lite, even in the regular length, is a little much. I think I would need the large x-therm (22oz) to get the same comfort that the original neoair would provide.

I think you could do it with that arrangement. I'm actually depending on less, and hoping to get by if I get a cold dip to 15F on one night or so.

Although I personally wouldn't want to do any extended length trips during 15-degree nights and sub-freezing days on frozen ground. If I was looking at weather like that, I'd take some more substantial padding.

One very good aspect of it is that you have a pretty decent layer of CCF in case the NeoAir pops. That's good for emergency contingency.
Another good aspect is that you can bring 1,2, or all 3,(or even none) of the Lawson pads, depending on your weather conditions. So, it's versatile, as you mentioned.

As for comfort at 15F, you'll have to try and see. Some people have done it with less, and other people have been very cold with the same, or even more. It depends on your particular needs, and if this system covers them.

It's a good thought process, and needs to be proven out in the field.
If you like your old style NeoAir for size and comfort, then this might be a way to continue using it into the colder weather.

The neoair short and CCF (cutdown to torso length) combo has been my winter sleep setup for the past two years. Last winter, I used it down to -10 F at Tahquamenon Falls in January, with about 1.5 feet of snow on the ground (extra insulation maybe). Seems like it shouldn't be warm enough, but for me it works. I do use a -20 F winter bag at these temps though.

For me, on snow, that would be a little less than what works. I use a neoAir like you have, on top of a CCF pad that's probably a bit warmer than your 3/8", on top of a 1/8" Suluk 46 pad that I use as a groundsheet in my floorless shelter. So I haveat least 1/8" of CCF above your system, and I find it just warm enough – I wish it was a little warmer. The thing about the neoAir is that yu only gt the full listed R-value if it is pretty firm – too firm for my tastes. So at the inflation I like, I'm getting less insulation. THe neoAir is very comfy – I really like it in the summer – but I'm not sold for snow camping despite the nice light weight.

But try it out. if it isn't quite warm enough you can always get one or two more of the Lawson 1/8" pads and like someone else said, take as many as you think you'll need for the conditions. I defintely like the idea of not relying solely on an inflatable pad on the snow. I have had leaks in the past – not with the neoAir yet, but with a thermarest in years past – and I was very glad I had a CCF pad underneath it to get me through the night. Plus, the CCF is great for a sit pad around camp or at lunch breaks on the snow.