That amount of filling is what books, pdfs, and your own computer are for. If you don't like the inconvenience of not having access to it at your fingertips, keep it in binders or notebooks you carry with you.
I really, really didn't want to influence people by requiring them to remove stuff from the defaults. Generic terms like "adposition" or "prefix" may not always be grammatically appropriate, since (for example) it would be weird to say "adposition" if the language only has prepositions. "Interjection," however, is already on the list, so what the hell, dude?
It would be quite silly to have a real-world mythology section here because, as has been noted, it wouldn't provide any advantage over, say, just going to Wikipedia or going to a real academic source.
The goal of having reference language stuff here is just to provide dictionary coverage for developing derived conlangs via SCA; I've only really let the project get as inclusive as it is because it provides a novel and useful conlanging perspective on the subject matter in some cases (e.g. the awesome German documentation written up by Querubín and Jípí) where compact tables would otherwise be hard to find or endemic, awkward-to-learn terminology might be preferred in the general literature.
You obviously have a lot of ideas for developing your own creations, though—why not focus your energy on that?