Thesis: supporting interchange formats is dumb. standards evolve but old software does not. sometimes developers don't care to do a good job or they are busy trying to push their own standards.
The best way is not to try and design an exchange format which is free and open (as ex. Fade In Pro does.) You should just provide the documentation for the file format you do use. Or alternatively offer a dump format that is designed around interop with user scripts which is easy to read/write and not meant for performance (as your main format is.)
People who have an interest in exchanging content with something else can write tools to exchange between the dump format and the interchange format.