While I really like K&#x2F;Q&#x2F;J&#x2F;APL (some of this is Stockholm Syndrome: I spent the first 3 years of my career writing K&#x2F;Q at a trading firm, eventually becoming the human debugger for my team&#x27;s K&#x2F;Q &quot;investment&quot;. It got so annoying that I worked on a little parser library to help me debug: <a href="https:&#x2F;&#x2F;github.com&#x2F;kiyoto&#x2F;ungod" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;kiyoto&#x2F;ungod</a>), they are doomed from a adoption&#x2F;future viability point of view.<p>1. Steep learning curve without benefits: APLs like K&#x2F;Q&#x2F;J optimize for concision to the point of unreadability. Sure, it might be fun to decipher clever K&#x2F;Q one-liners, but if you have to do it everyday for work in production, it&#x27;s just exhausting. This lack of readability has limited adoption and the growth of its user community. For any technology is to have a viable community, it needs to be usable by a critical mass. K&#x2F;Q in specific but APLs in general never had that, especially with more user-friendly alternatives like R&#x2F;Matlab for scientific computing.<p>2. No open source community. There&#x27;s Kona (<a href="https:&#x2F;&#x2F;github.com&#x2F;kevinlawler&#x2F;kona" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;kevinlawler&#x2F;kona</a>) by Kevin Lawler, but again, its community has been small because the underlying language is not design to be usable by enough people.<p>3. Domain specificity of array languages: These days, array languages are just too limited in its scope. Scientific computing, the bread and butter of any array programming language, has been made possible in other languages (ex: Python), making array languages not powerful nor compelling enough to use because most of its strengths can be found in other languages and its weaknesses are too crippling.<p>I heard that Arthur Whitney found his successors (a pair of Russian programmers from St. Petersburg, iirc), so K&#x2F;Q will likely to be around beyond his retirement. That said, I think its user base will continue to shrink for above reasons.