It had to happen, I finally got around to reinventing the wheel.
Rather than persisting with that simple old round geometry, today’s invention is a way to have wheels (top of the image) transform themselves into tracks (bottom of the image) by varying their internal geometry. The suggestion is to do this by using an outer track with driver wheels raised off the ground in both cases. Idler wheels would be moved radially inwards or outwards within slots to create a circular arc or flat profie (or intermediates between these).
In the wheel case, the idlers might even be locked in position around the circumference of a circular hub, so that the whole thing could roll, effectively using the track only as a wheelrim.
This would provide, when a wheel’s low-rolling and turning resistance weren’t required, a better response in terms of grip and load distribution.
Someone has now built a version of this (although they seem to be using extensible tracks and only two idlers, in a rather complicated mechanical system -but it certainly works).