[anyfoo]

I have asked this question in interviews before, with focus on low level OS aspects. It depends on whether your made-up OS includes the things we care about.

I usually ask the question in an open way, but guide the candidate to "fast forward" past the (for us) boring parts, and focus on the interesting parts we are looking for along the way.

If your OS covers the concepts we are looking for and the answers seem competent, sure, let's give it a try, but don't be surprised if we veer off of that. If the OS is too simple to cover everything (not unlikely for actually existing toy OS projects, I have one myself), we'd want to branch out to those concepts no matter whether you included them in your hypothetical OS or not. And if your made up OS is just too different, it might not apply either.

In other words, ask yourself why this is part of the interview, and that should answer your question: Because you are going to work on a particular OS with particular characteristics.