I'll have to disagree. The primary motivation for J was that APL could not penetrate into mainstream software development because the world-wide installed base

I'll have to disagree. The primary motivation for J was that APL could not penetrate into mainstream software development because the world-wide installed base of IBM PC or clones simply could not deal with the character set without much mucking around. It went as far as having to purchase very specific graphics cards so that you could swap out the character ROM. BTW, when I say "graphics cards" the mental image should be a very primitive character-mode only VGA card that is stone age when compared with today's cards. In my experience it is difficult for non-APL-ers to truly understand just how bad it is to lose the symbols. The only approximation I have been able to find that clicks with some people is to compare it to musical notation. Anyone who reads musical notation understands the value of symbols very well. I can't relate to the idea of writing code on a mobile phone. I have never done anything that useful, even with my iPhone X. I barely want to reply to emails with it. I wrote a paper for an APL conference back in the dark ages. Printing the paper with APL characters as well as normal text entailed a double printing process where I had to change the ball on the IBM printer between APL and standard characters. I actually wrote a custom print program (in APL, of course) to manage the entire process and, of course, wrote the paper in APL using a custom text editor I wrote as well (Wordstar couldn't handle the task). Think of it as Jupyter Notebook (but not as sophisticated) for APL. Ah, the good old days when you had to create all the tools you needed yourself! Another way to look at it is: Had Iverson focused on advancing APL to the next stage, computer systems would have caught-up with the language. My guess is that the economic viability of his business forced his hand. I can understand this, of course.