Very good point on packed volume.

I started with closed cell foam half a century ago for camping, switched to self inflating pads about a quarter century ago for the comfort when camping. Then a bit over a decade ago bought an air mattress without foam because it fits in a pannier better. At that time, the packed volume was the only reason that I bought an air mattress, it was even slightly heavier than my self inflating pad. Kept using the self inflated pad for backpacking and canoeing. But in the past couple years stopped using the self inflating pads for non-cycling trips and switched to air mattress for comfort.

The only time that I used a closed cell foam pad for the past couple decades was for snow camping, put that under my other pad or air mattress for insulation.

Vast majority of my camping is in areas without thorns, thus I have not had to worry too much about ground sheets or putting a foam pad under the air-tight pad/mattress. I did a week long van supported trip with ACA in West Texas a few years ago, they specifically recommended a foam pad under any air mattresses due to thorns. I rolled the dice and did not bring one, did not have a puncture but I was very careful when setting up my tent and packing it later.

When I first started touring (over 36 years ago) I used a foam pad, I could sleep on it. Fast forward 36 years and now I can't get comfortable on a foam pad, plus honestly the take up a lot of space.

I probably could sleep on one, but my neoair is so comfortable I am not inclined to try. As far as taking up space, that may or may not be an issue. Strapping it on top of a rack or outside the pack when backpacking it may be a complete nonissue for some. Others may be bothered by it. It probably depends of whether the space is needed for something else. Also for a rackless system there may not be a place for it.

The newer backpacks do not have as many lash points for that sort of thing compared to the vintage packs we used to use.

I could do that with my older packs, but not the newer ones. My old Tourpack below.

https://cimg3.ibsrv.net/gimg/bikefor...4aa26a0ce7.jpg

I still see quite a few folks with one of those folding pads lashed on, often vertically on the back or side of a small pack. Not so often across the back like your picture or under the top flap like I carried mine decades ago.

I see a lot like this on the Florida Trail.
https://cimg8.ibsrv.net/gimg/bikefor...52a6d8749b.jpg

I do not see that many of the foam pads used here. Maybe there are not enough thorn bushes to discourage inflated pads and mattresses here, most of my camping is in Minnesota and thorns that can puncture air mattresses are quite rare.

My recent trips were on Superior Hiking Trail, there are no shelters with hard floors. But I have done a few backpackign trips and also kayak trips on Isle Royale in the past decade where there are a lot of shelters with wood floors, and that hard wood floor is REALLY hard if you do not have an air mattress. My first trip there I had a thin self inflating shorty pad and that was a mistake.

I have switched to an air mattress for backpacking, partly because of ease of stowing it in the pack and partly because it is more comfortable. I do not have a good photo of the backpack I started using a couple years ago, this is a stock photo of it off the internet, but mine is green.

https://www.rei.com/media/6dbbe106-8...f?size=784x588
It would be possible to strap on a foam pad like in your photo, but it lacks those convenient lashing points that the older packs all had. If you lashed it on like on yours, you lose access to some of the pockets. This is a Traverse 70. I am sure this is much bigger and heavier than you would use. More here:
https://www.outdoorgearlab.com/revie...op-traverse-70

It is something I have only seen much pretty recently. I haven't backpacked for a while and when I last did it was in the Sierras. The ones I have seen lately were section or thru hikers on the Florida Trail which passes by not too far from where I live. I don't know if those pads or carrying them that way are popular with thru hikers on the AT or PCT these days. They would be light and trouble free.

I can vouch for the comfort of the Nemo Tensor™ Ultralight Sleeping Pad Series but I have only slept on it a couple times so I can’t vouch for longevity. I have the Long Wide, which is 76”x25”, so it is relatively roomy.