Would you consider adding support for PostgreSQL instead of just MySQL. I realize that it can greatly complicate things, but PostgreSQL is generally a much better DB.
This is answered in some detail in the post :) Ghost uses Knex and Bookshelf, and can work with any database that is fully supported and made interoperable by those packages. So if anyone contributes to the upstream repositories, the Postgres will work automatically. The core Ghost team focuses on MySQL because we're a small team and we can only really have the resources to document and support one environment properly.