I'd love to have APL or K on a small calculator like the HP-15c just for the cool factor. With an SD card slot it would make for a really cool portable programming computer.
The physical keys is why I still grab my 30ish year old HP-11C for quick experiments, however it's hard for me to phantom a good experience with K on a single line display. We'd probably be better off with a portrait form factor, roughly 1/3 display, 2/3 keyboard. Getting switches with the HP quality and feel is the biggest problem.
EDIT: actually, porting oK to the DM41x might be the best option (putting stickers on remapped keys).
Closest I've come to that so far was getting oK running on a PocketCHIP. (Which is really just a matter of installing node and cloning the repo, thankfully.) The keyboard is less than stellar, but not too bad for trying little expressions.
