I'm not sure but I believe those "conventions" boil down to preferences. So, it's all about giving it some thought, proposing a change... and then have an actual "code-base" / pull request to talk over modifications such as "let's better use this name, rather than that one". Tbh, I am not sure what those conventions are when it comes to field-names or if there really are any (yet).
All I'm saying is that you can literally propose changes to core macros as you can propose changes to the core documentation. The process is very much the same, if you so wish.
Ah, interesting. Didn't know that was the background. Glad to see his course catch (your) interest. I have to admit, I haven't taken much time yet to actively part-take in any of it. I very much like the slightly more scientific setting so as to explore the TiddlyWiki ecosystem and habitat in all its expressions from a duly conceptual / analytical perspective... while doing practical and quite useful exercises for it all ...such as this one.
I'm sure the goal of it is not to birth "TiddlyWiki developers"... but perhaps it helps people see that the process of that truly is just that: doing the desired changes while coming to terms with why and what and how to do it. Could just be a part of your note-taking process... but could also be a little something that ends up benefiting the community at large.
So, I think, this kind of "contributors-mindset" is very welcome and worth nourishing. It's not so much a privilege to do the "actual developing"... but rather something you dare undertake, exposing your ideas and solutions to the scrutiny, eventually of the one(s) who designed the core aspects of the ecosystem.
For what it's worth, I am pretty confident there already is (/are) some GitHub issue(s) about the topic of (more use case oriented) captions... for you to chime in, if you so wish. Contributions need not always be in the form of code, but can just be a distillation of an idea ...only later turned in to code.
Take Mat's federation. He had that hunch, as he often does, coupled with plenty excitement as well as persistence... and eventually it lead to the advent of it all, even if he may not have aspired for any code contributions on his end.
As said elsewhere, there are those that just go play ...with ideas ...and then some to work out the whys and then those that formalize the whats and eventually those that figure out all the hows. All of these steps are important by themselves and having them be impersonated by one guy is quite a rarity, cough Jeremy. ;-)