And/or sell the service where you BYO keyword list and this ranks them. Keyword lists can themselves be scraped from forums and websites in the marked the client is interested. The scraping could also be an add on service.
This would lock in nicely with the keyword research that ahrefs, moz, etc. offer. And other various colour hat seo software.
Selling the data as an API is definitely a potential. I was originally thinking to allow CSV downloads of the data. Would an API be more useful for your client's use case?
You seem to have done most of the hard work, collecting the data. I'm not sure they'd care what format the data was in. Providing it could be expanded to cover the topics their clients need.
This would lock in nicely with the keyword research that ahrefs, moz, etc. offer. And other various colour hat seo software.