Interesting article. I'm playing with J currently and it is one powerful, yet difficult to learn language. Simple things are simple, but being able to efficiently chain trains of verbs together and think not in terms of loops and normal data structures, but arrays and math/matrix operations takes some training and time to get used to. I'd like to keep it up to obtain a powerful data analysis tool in my arsenal, but I want to make sure there are enough J & APL developers to make sure it is worth it. The language itself is amazing, but if there aren't enough developers you start to suffer from lack of libraries and you end up back in JS/Java/Python/Perl land.