@fgeorgatos: The above looks great as a cleanup, please include this in the PR.

Just list the extensions we currently have, and the ones you want to add and for which we have support in `extract_cmd`.

You don't need to look into all the fancy extensions you mentioned yet, but I won't merge this in until @stdweird's remark has been acted upon. If you touch code that could greatly benefit from a cleanup, you should do the effort of the cleanup too, otherwise stuff never gets cleaned up (trust me)...