A friend of mine is a bullet journal fanatic, and shared your post with me after we had a conversation recently about using one to keep track of writing ideas. :)
I also use a Passion Planner, like one of your other commenters, for my daily/weekly to-do and schedule, but use various notebooks for writing, trying to just use ONE at a time — but that gets difficult when I have ideas that pop up and I don’t have time to act on them. I have begun using the washi tape idea to mark things I want to come back to, and had the idea of using specific ones for specific stories in progress that I might have a thought about and jot down while I’m not at my desk.
Anyway, ramble, ramble, I appreciate the post!