i think the golden usecase would be running thirtybees on heroku (postgresql, composer, php 7)
EDIT: there was a dead comment about how postgresql is not good. what im asking is different - im requesting for an ORM like Doctrine or Propel. This will let the end user choose the database that they want to use. But you have to take this stand pretty early in a project's life cycle or you will not be able to do it later. Exactly the issue with WordPress.