Mainly, I'd like to see air chambers that are oval - not round in cross section.
The reason? Lower sides with the same buoyancy = more elbow room WITHOUT rising both seat and of occupant into a wind catching position.
I assume it could only be done via two bladders inside the chamber, and a vertical section of fabric joining top and bottom to compress the bladders vertically so they spread out to the side more.
As a second idea I suspect we drag too much surface water along with us in triangular (viewed from above), vee, and round tubes. This increases effort and decreases speed.
The framed pontoons are much faster because their tubes are lengthways in the water, like the hull of a kayak aligned with the direction of travel, but of course pontoons are high and prone to excessive wind drift (being high but with no keel element underwater to counteract drift).
So I have wondered if a tube that has the seat flush with water surface (high enough to reduce water drag, but not an inch higher) with wide low pontoons, and a nose clear of the water to let water through and not push it aside and drag it along behind, would be the key to the best allround performance float tubing with fin power.
The Fish Cat Panther manages to do this with 10" tubes which are a lot lower than the 16-18" tubes we assume to be necessary. Imagine a Panther married an ODC420 or Fish Cat 4 and had a tube-child!
Norm