Still, can we mod anything about BG3 even without the editor?
There are various tools pinned on Discord in regards to unpacking .pak files, so anything not relying on osiris/anubis compilers there is readily moddable, but not supported by Larian until full release. Norbyte also has a beta for his BG3 extender which may allow for some lua scripting as well, however I haven't gotten around to try it out myself yet.
B) Document and tutorializing the whole thing in a way that makes it actually usable, otherwise it's like borrowing a college textbook about calculus to a middle schooler.
BG3 is mainly "Anubis" (lua) and Osiris, both has pretty solid documentation already as far as scripting goes. Other engine features such as dialogue editor, quest journal etc is fair to expect to be rather straight forward and intuitive based on experience in older engines.
Hmm... if the team has some kind of editor, why not share it with fans then?
Larian has confirmed modding support for "at or after full release", but what that entails isn't elaborated upon. Many assume this means access to the new version of Larian's engine similar to Dos2, but there's no details public about exactly what to expect or hope for yet.