There was a time, when I was so fed up of the Calibre being so bloated, while all I needed was just a convert capabilities, that I started to rip off parts of the Calibre, clean it up, make things simpler, removing unnecessary things and trying to understand what is happening behind the conversion, resulting with ebook-converter[1], which simply do the conversion, without all the management/downloading rss/editing/what have you. It is usable right now, but I'd say it's still somewhere in between alpha and beta stage. You could give it a shot.
looks like an interesting project... but I must admit it's not really something I use or need anymore. I used to do some book conversions when I would only find (say) a `azw` or a `mobi` file and would need to convert to `epub` but these days (a) I just find a `epub` but even if not (b) koreader can read `mobi` files and a lot more i can throw at it and (c) `azw` files are basically unconvertible, if I followed that correctly.
I own really old ebook reader, but it still works (Sony PRS-505), so mine intention was to be able to easily convert to BBeB/lrf format, which is fastest on this reader. And no, I didn't bother to find out if drm can be removed from the ebooks - perhaps the reason is, that I'm always looking for drm-free ebooks. Although, I don't mind if anyone want to implement that and contribute.
[1] https://github.com/gryf/ebook-converter