I dig it! FMA is such an exciting world of trouble and power, so an RPG adaptation makes a heck of a lot of sense to me.
Favourite details: Oh, the Rebound Die, 100%. The way it plays with both forbidden knowledge and the temptation to seek it -- as well as the consequences for doing so -- is a great little spice to add into the standard roll resolution. It's simple, but carries a lot of weight to make the system stand out and do something unique.
Best of luck as you develop your next version!