Yeah, that’s something I’ve thought about, but once there’s TPU on both sides of the standard tube fabric then it’s only slightly lighter than the standard 450 GSM floor fabric – the difference isn’t big enough to make it worthwhile on a floor that’s about one square meter (it might save 50 or 100 grams compared to using the standard weight floor fabric). It might work to use thinner TPU coatings, but until I hear about people actually puncturing the ultralight floors (as opposed to being worried about it happening) then it’s probably not going to be a priority.
Also keep in mind that the floor inside the cockpit isn’t required to keep the packraft afloat. I’m currently developing a self-bailer and the platform is a Skeena with a bunch of holes cut in the floor. When I paddle it, the water only comes up in the cockpit a couple of inches and it still performs fine – the tubes provide way more than enough flotation.
One possible option for the Ultralight would be to reinforce the floor fabric where it’s exposed inside the tubes by heat sealing a layer of tube fabric over it… but yeah, I haven’t heard of anyone puncturing an Ultralight yet, other than me when I was doing something stupid (to see what would happen, I let myself get pushed over a small log jam in a shallow stream and the current basically impaled me on sharp sticks – easily avoidable).