Am I wrong (and this is of relevance to a recent thread by Flanna too) but didn't the CBA evolve when someone rearranged the reeds on a 3 row diatonic?
It seems to me that where you want lots of flexibility for cross rowing and right hand harmony, the CBA is the logical evolution of the melodeon. Perhaps one way to go is smaller lighter CBAs. I have a suspicion that the lack of bounce on a CBA is as much down to playing style as to the inherent characteristics of the instrument. There is nothing to stop you using bellows changes on a CBA particularly if it is small and light.
Just one reservation about Jon's ingenious layout is that a 24 bass is going to be significantly heavier in the Bass end than an 8 bass and that will affect use of the bellows more than the total weight of the box.