I have used K for multiple interview and take-home programming questions. The use of K always raises interesting questions such as "Where is the code?", "How does this work?", "How is the K executable so small?", and "Why is it so fast?"
Awesome. Great way to assess the interviewers at the same time they are trying to assess you.
Yes. Using K is a great way to see how open-minded the interviewer is and how they respond when they are outside of their comfort zone.