I think this type of usage is rather common, at least the way I used property tree relied heavily on these features. For example I used it as a primitive serialization library where files containing objects were human creatable. I had an application which had GUI to manipulate these objects, and allowed to save them back again to files. All I/O was done using property tree.
This type of usage require different tools. I would use Serialization lib for that.
What I think PT must have that serialization library is not meant to is: 1. The ability to load/save properties independently, not as a whole. 2. A documented (for library extensibility) parser interface allowing parser developers to accomplish (1). At least 3 storages requiring (1) come to mind: windows registry, ISA Server storage and IIS metabase. I would put these requisites as conditions for acceptance. Best regards Jorge