How would you go about this?
Appart from the Inventory and the parsing of your Playbooks you could come up with a Play/Role that create Documentation based on Templates, Facts, variables and stuff, utilizing the setup module you could build a generic drop in System.
Oh, also this might be of use for you https://github.com/fboender/ansible-cmdb (did not test it myself though!)
Moytura. Destroy the old gods.