I understand the hesitation, it's a difficult one, but thanks for asking our oppinion.
I bought this course for the 4.0 update and tbh I don't see a LTS version coming soon. So if I were in your shoes, I would probably aim for the next stable release that I know I could get this update done and communicate it. So either 4.1 or 4.2.
And obviously, I hope it will come out sooner than later :)