I have nothing useful to add for what resources to do next, I just wanted to say: This is an awesome piece of software you've made. Great work.
Edit: Thought of two possible ideas, but I have no idea how much either are economically viable. First: A more sombre, gothic tone, akin to what Mechanicus' soundtrack sounds like. Pipe organs, violins, chants, that kind of thing. Would really give a different tonal option than what's currently available.
Second idea: Packs featuring a bit of a "regional identity", like a Chinese, Japanese, Egyptian or Latin twist. Might be cool to play around with as well.
Again, awesome work!