I think the problem here is the same one as the other current music generation services. Iteration is so important to creativity and right now you can't really properly iterate. In order to get the right song you just spray and pray and keep generating until one that is sufficient arrives or you give up. I know you hint at this being a future direction of development but in my opinion it's a key feature to take these services beyond toys.
I think it's better to think of the process of finding the right song as a search algorithm through the space of all possible songs. The current approach just uses a "pick a random point in a general area". Once we find something that is roughly correct we need something that lets us iteratively tweak the aspects that are not quite right, decreasing the search space and allowing us to iteratively take smaller and smaller steps in defined directions.
I think it's better to think of the process of finding the right song as a search algorithm through the space of all possible songs. The current approach just uses a "pick a random point in a general area". Once we find something that is roughly correct we need something that lets us iteratively tweak the aspects that are not quite right, decreasing the search space and allowing us to iteratively take smaller and smaller steps in defined directions.