Awesome @jesta!
I have a few ideas for other Steemit related services I have been mulling around in my head and it seems every idea I come up with the current API is a major design limitation. It's just too difficult and expensive to get at older data.
The only way I could think of to solve this is to pull every block and parse the information I need into a local db that is optimized for the searches I want to perform. I haven't had the initiative to attempt that though, and now you have gone and done it. Superb!
I look forward to looking over the code when I have the time to see if I can integrate into my projects. Super good work man!