I use J quite a lot. I'm interested in why you're not keen about it?
Asking because I'm thinking of adding some form of array language to the statistical/data science Racket framework.
I don't know J as well as k, but it seems to map less to trading/finance, my domain of expertise.
I like that k/q is a more traditional language in a sense, you can write code (if you have to) that looks like regular functional/imperative code. J is more obtuse and takes a more mathematical approach that can be confusing.
I do like forks and the point free style though.
I love k/q and see a lot of the ideas of array languages perculate into the mainstream thru numpy and Pandas. However, both are really shitty compared to a true array language.
I personally love k/q, J I'm not as keen about.
I've also created my own array language called xs: https://cryptm.org/xs/ I don't really work on it anymore, but it might be interesting to some folks researching/developing new array languages.
I think there's a lot further we can, and k/q definitely has a bunch of warts that hopefully shakti/k9 will solve.
I really want Shakti to have lexical scoping, and I feel like too many compromises are made for performance/simplicity reasons that reduces the ergonomics of current array languages.