This comes to me just after an extended weekend reading up and mashing data around frequency lists. Are you open for collaboration with other language tools? I'd love to be able to import your word study lists, for instance (my tool ain't live yet).
Thanks for checking it out. I haven't gotten around to creating an API yet, but I am very interested to learn more about what your use case might be and what data you would like to be able to import, etc. Send me an email (my screenname at gmail.com).