When I see instructions that say “This project tests your ability not only to code, but to deal with ambiguity and open-endedness”, it actually means either a) this exercise has been so poorly conceived that we didn’t bother with a rubric or b) the work environment is so chaotic, we never clearly define specs or requirements for anything.
That, and the instruction to simultaneously “show off your skills” and deliver a pragmatic functional solution are completely at odds. Good simple solutions aren’t flashy.