Didn't make it to the end?
Again, I read the entire article and saw he ended up with a generic solution.
The article wasn't interview advice, it was advice about avoiding premature abstraction.
The goal is getting the job, or being a smart ass?
As an interviewer, I'll put this one to bed. Pick up the white-board marker and start writing.
The intern can look up libraries; I want to see if you can understand what we'd be looking for in those libraries. If you can't implement and discuss a simple version of it, odds are that you cannot.
If during this process you talk about how you'd be starting a build/buy research cycle at certain points and what that'd look like, as we spec out the problem and build a prototype, that wouldn't be misplaced.