Unfortunately, as much as I would like to see this addition too, I do not see this happening soon (at least not with the current pace of community growth).
Over the next months I feel we should focus on improving the usability and robustness of what we already have, before adding new applications.
This is not to say that if someone comes with the addition we wouldn't happily goo-it in. There should already be some simple GPL billing apps that could be re-used to achieve this without starting from scratch.
Another possibility is finding someone interested in sponsoring this, so that we can add more coders to the team.
Ideas?