I've released a Config::Model 1.206 which feature all the work done so far by Krzysztof Tyszecki during this summer's Google summer of Code. Here's the Changelog:
First version to feature code written during Google Summer of Code 2010.
For this GSoC, Krzysztof Tyszecki has provided:
* a new backend for INI file that can:
* read and write comments to and from annotations. This way users comments are preserved
* read and write parameters that are repeated in the INI file. This repeated parameters will be loaded in list elements
* the capacity to load annotation from perl data structure
* a new model feature to accept unknown element. This will enable loading and writing configuration files even if parameters are unknown. This feature is required to create models targeted for configuration upgrades: only upgrade and migration specifications need to be specified in a model. Parameters that don't change from one version to another need not to be specified in the model.
* lib/Config/Model/Loader.pm (_walk_node): bug fix to load node element annotation
* lib/Config/Model/Dumper.pm (): bug fix to dump hash and list element annotations
* Fixed Fstab example
This probably does not mean that the configuration upgrade problem is solved, but that's certainly a step in the right direction.
All the best