If you're a dev, forking Ghost and replacing the DB with something else isn't an insurmountable task.
Your prep work in isolating the database work may even be something the Ghost people themselves would be interested in merging, as it's just good design to do so (if they hadn't already).
[1] https://github.com/TryGhost/Ghost/blob/master/package.json
[2] http://www.howtoinstallghost.com/how-to-install-ghost-on-her...