To add support for another type of storage you need to create file inc/class/BxDolStorage1fichier.php and implement all necessary methods to add/get/delete/etc files. To get list of methods you need to implement please refer to inc/class/BxDolStorageS3.php. 

When it's implemented you need to update 'engine' field for the storages where you want to use your custom storage engine, more info here - https://github.com/unaio/una/wiki/Dev-Storage