@traq, +100% my initial thought was they’re more interested in the process rather than the actual solution.
I was tasked once with similar pre interview request, after completing work I was invited for the interview. Everything went great, felt like I had the job. Week later I received a call saying the funding for the position has been cut. Now I don’t think I got played, but thought did cross my mind.
Just be careful of request that just seem ridiculous. My task was to slice up PSD for a landing page and convert it into HTML. But your request seems like you will need a lot more time than what I invested.
Hope that helps and good luck with the interview.