The preview is feature-complete within itself, so it is ready for play whenever. The preview is most likely going to stay just that, admittedly, considering whenever I attempt to work on this I hit the brick wall of determining a set scope for the project. While there could certainly be more traditional rules (such as advancement) and set options for character creation, FMA has such a variety of characters it'd make the project a massive undertaking. In that way, I'm kind of content with it as a one-page RPG, for now.
Thank YOU!