How about abc text files? will they work?
Biab can export and import chords from abc files. However I don't know if it covers all details needed (variations of chords, time positions within the bar etc). It is very easy to test, populate biab with chords on the finest level and with the most complicated chords available then save special abc. And redo with open special abc etc, Also open and modify the text file to see if the changes loads correctly. But maybe it is very buggy, there were a lot of problems importing abc files when it was launched some years ago so I stopped using it.