The cooker now has finalized configuration metadata available, so we should consider including this metadata in the ConfigParsed event, as it's quite common to have to create our own copy of the metadata and finalize it in a ConfigParsed event handler. Also, expanded_data is not named well. Expansion isn't greatly relevant, other than of metadata keys.
Since we're looking at trying to get rid of update_data entirely, I'm holding off this whilst we explore that...
Since the data store changes merged, this is now resolved as the data store doesn't have to be expanded (http://git.yoctoproject.org/cgit.cgi/poky/commit/?id=a730981b75ebb528e447eb3e41c83440dbc133bd).