One of my friends has an airframe, he broke it the first time he sat on it due to him being too heavy for it. I am yet to see one in the flesh so dont want to be too critical of it until I have.
i think there are good reasons why you dont see many...
flex,riding postion, chain line , folds poorly,
i have seen one riden. possibly by owner taking it to recycling facility.
i see your point cpg, some bikes can be made ok with mods.
i think there is a limit to reenginnering silk purses from designers sows ears.