A bit late on the reply, wonderful post, thank you for the mention. There are a lot of things I don't consider in the copyright department considering origami. In my opinion, which might not be a popular one, if an artist is openly sharing instructions of their works, it should be considered fine to post resulting works if you include the folder and designer in the title/description. asking for permission is always nice but sometimes it can be worrisome for more popular designers who suspect ulterior motives or have a language barrier leading to misunderstanding. Seeing the end result and asking to take something down if not appropriate seems like a better option.

ps. I'm working on something you might enjoy, here's a preview :D