It seems to me that a track wheelset would need to be axially stiff but not necessarily laterally stiff, since you are not going to be making sharp turns on the track anyway. If you rock the bike heavily side to side in a sprint, you might laterally flex the wheel, but if the flex is so large that it is a problem you are probably rocking the bike side to side too much to be pedaling efficiently anyways.

There are plenty of lightweight, stiff road wheelsets that can be had for <$500 MSRP. So what's stopping somebody from lacing a track hub to one?