The biggest issue you'll run into is once you have a cable made, does the protocol for the eclipse changer bus match any other manufacturers currently supported protocols or not.
If the answer is no, this project would be a waste of time due to the phatbox's microcontroler (the 8052) software (the flash updates you get from phatnoise only update this little controler and the files on the harddrive) being specific for each type of head unit.
They emulate the CD changer commands and responses using the 8052 so if kenwood uses another set of commands or a changed structure etc you couldnt use the kenwood firmware for instance. Rinse and repeat for other firmwares..
I would say its highly unlikley that we'll be able to add clarion or eclipse support to the list without significant additional effort.