Regarding selling TextFugu past the point of Koichi giving up, my experience might be relevant. I received a lifetime membership to TextFugu as a Christmas gift in 2016, so it was bought October/November of that year at the very earliest. It was my fault, since I hadn’t read into it enough to know that it was obsolete the moment I considered getting it. At the time, the pricing page didn’t have any notification that the project was dead in the water, from what I remember. Hell, it’s still not clear in the textbook itself what the word on future developments even is.
It definitely doesn’t feel right to me how rough around the edges chapters 7 and especially 8 are. It was extremely unceremonious to realize that there wasn’t anything left when I completed everything, except for an advanced lesson and a massive vocab deck which felt like a bit of a cheap cop-out for actually introducing them over time via more lessons and content. But like it’s been mentioned earlier, Koichi has his cash cow in the form of WaniKani, so there’s little incentive to go back and update the textbook almost everyone has moved on from.
Something interesting at least is that the current pricing page says that all lifetime TF users will gain lifetime access to EtoEto when it releases. If it releases, anyway. I feel like that’s somewhat of a cherry on top of what has been a disappointing service for TF. Then again, if EtoEto languishes in development hell for another half decade or two (or three), we’ll have all passed the N1 and beyond and it won’t be good for much.