It's very easy to customize either via plugins with Rust or by overriding template files. While the linked article is cool, it seems like a lot of effort to maintain such a set up. Then again, if you're a Ruby expert I could see this being worth it.
Also, sometimes I start writing scripts for simple things, then they grow and at some point it's interesting to share them to my teammates, and they all immediately dismiss it since it's in Ruby. For that reason, I started doing all my work-related scripting in Python. But oh boy, it's always with that sad feeling of "I wish I was doing this in Ruby". Sometimes I think I should just not have learned Ruby and jumped straight to Python.
I don't do any ML and don't know much about it, but the Elixir / Phoenix people around José Valim now build ML software (nx, livebook) and I'm excited for this.
So whatever headstart Python might have in machine learning, it is only a matter of time until all major languages support the same C, C++ and Fortran libraries.
The only things holding it, are having anyone that cares enough to write those bindings, and the culture of which languages are accepted when submiting papers.
I'm not entirely sure why Python got its initial edge for data processing. I think Google probably played a big role by sponsoring Guido and making it one of the key languages used internally and on App Engine. Ruby also had its share of drama and not everyone appreciates its "More than one way" (TMTOWTDI) philosophy.
I grew to love Ruby, though I admit I always approached it with half a mind pretending I was writing Perl.
These days I've sometimes fallen back into Ruby, but then had issues sharing it with colleagues - so I've largely switched to Go. While most people don't have a dev-environment setup I can give them binaries built via github/gitlab/jenkins, and so sharing tools & utilities is just that little bit less painful than with Ruby (and even Python).
Obviously Perl came far earlier than Ruby and Ruby was heavily inspired by Perl (There's even a quick comparison on the official Ruby site here https://www.ruby-lang.org/en/documentation/ruby-from-other-l...) but it always felt like Ruby is such a nicer language to read and write and obviously due to age was just a more modern overall. You could define a class as a... class!
Whenever I wanted to make a quick script for myself for personal usage I'd always write it in Ruby.
I'm now in a C#/.NET role and love typed languages now but I'd never go back to Perl, but I still have a special spot for Ruby.
The thing is that is an issue of community, because Ruby does have an FFI and there is really nothing stopping people from building libraries similar to how they're done in Python, calling out to C. They just didn't.
It's hard to remember more examples. I remember having problems even with FastCGI on Ruby, but I ended up not writing the code at all so that won't count. Also something related to parsing emails.
The older and more boring I got, the more I liked Python. Young me and old me both knew what they were doing.
I'm also a big fan of the HexaPDF library: https://hexapdf.gettalong.org/
If you want to just convert files, you might try the File Transformer by Blackboard Ally. They've licensed the BeeLine technology and are temporarily making it available for free publicly through the File Transformer (it's also available to their university customers through their LMS interface).
Lastly, I know it probably won't put your mind at ease, but I am the solo founder who runs BeeLine Reader. I do not do anything with user data, and in fact I don't even gather data at the individual user level. This is partly because my tools are used in K12 schools, and partly because I can't imagine selling out my customers.
You probably know better as you have probably done some business modelling but just for my piece of feedback - I would buy it if you would offer a purely offline Linux+Windows+Mac app that outputs coloured (and structured) PDFs given a MarkDown (or some XML intermediary, perhaps FB2, for more complex structures) file and a paper format for input. At the moment I feel like the price I would pay could be something near $100. I wouldn't even mind paying if it's just a proprietary script on top of free software.
It would also be great if one day you would add an on-demand (on the extension button click) mode to the extension to save the users' CPUs and batteries.
I hope you don't feel insulted or discouraged by how do I speak about your creation's performance - I understand it can be hard to teach a browser's text rendering engine a totally new trick. Perhaps you have even improved it since the last time I tried (which was years ago).
In our experience, the group that favors autorun tend to be the ones that get more benefit out of our software, and therefore are more likely to be paid users as opposed to people on the free trial. Because of limited resources (and the need to make the product simple), that means we've focused on optimizing for the autorun case instead of the manual activation case.
I should note that we do have a way to use the extension just as you describe, which is to use the Clean Mode. This is manually activated using a keyboard shortcut (which is hard-coded in Firefox and manually configured in Chrome). If you turn off autorun you can invoke BeeLine (in Clean Mode) using the shortcut.