I found out about Markdown Preprocessor (MarkdownPP) which generally enables this feature.
Admittedly, I have no deeper knowledge of JavaSript let alone how Joplin is programmed and this might too big of a change (and/or an undesired dependency) but I'd really fancy this feature. Could also help here.
Edit: there is also a fork of MarkdownPP which was rewritten in JavaScript. It can be found here. It does not seem to be developed anymore but it has an MIT license, so using the code shouldn't be a problem.
The implementation looks fairly simple. but I don't know how easy it is to incorporate that into Joplin. As I mentioned, I don't have too much knowledge of JS but if someone was willing to provide some help and point me in the right direction, I might give it a try.
I'm currently writing my thesis and having the different chapters in different notes really helps with keeping things organized. Moreover, having a little side project is a great way to procrastinate! 