I wrote 10 books for conventional publishers (Springer-Verlag, McGraw Hill, Morgan Kaufman, J Riley) but burned out on writing. What made writing new and fresh for me was a few years later starting to self publish. I sell far fewer books but I find it much more satisfying writing exactly what I want, not what publishers’ market research dictates.
I stopped publishing physical books, via the excellent Lulu service, because a physical book freezes what I can do with the content. I use leanpub now to publish eBooks and I can effortlessly fix small errors, add examples, and sometimes declare a new edition by adding material and removing out of date material. The platform lets readers get the updates for free. I also started releasing my eBooks with a Creative Commons share with no modifications or commercial reuse license - I encourage readers to share my books with their friends.
The author of this article makes a good case for using an email newsletter. I generally only spend about two hours a day writing and I am not sure if I want to spend some of that time on a newsletter.