One of the big problems with an adapter is pretty much every one would need to be custom made to match the treadle to the head. It might work to some extent if you had say an adapter to drop a White Rotary head into a Singer treadle base or the other way around but it still leaves a lot of older less common makes hanging out to dry.
Probably the best universal stand would be something like the old Singer convertible setup where the carrying case bottom fit in the treadle top. Something like that would be a good option. All the boxes would need to be the same size and the pulley would have to be in the same place but by the 1950s that was pretty close to standardized anyway.
Rodney