I might say something stupid, but what about aAn XML dialect, like GML? It's defintely, is definitely not optimized to operate huge datasets, but, can be used as an exchange format between software or between platforms, why not?.
I don't believe there is any problem with the licensing (see Ragi Yaser Burhum's post about the viral characteristics of Spatialite) and it is fairly easy to adapt existing parsers if required...