Let me preface this by saying that I recognize it's both too early to worry about interviews and this probably shows just how much more I need to do to get ready for the job market. In response to Philo's question, one commenter said:
"Try to get them to ask some general questions, (what makes this project interesting? relevant? how would you explain this point to a non-specialist? What kinds of publishable works can be extracted from this? What comes next? etc.)"
I get why departments would be interested in your future research plans. I can see how showing that you can frame your dissertation in different ways may further show that you can converse with philosophers outside your area. But, I hope questions like 'what makes this project interesting or relevant' are mostly intended to get the interview started. When I think about answering the question I get this image in my head of a 10 year old going, "so what .. so what .. so what .."
Maybe you're just supposed to use the question as an opportunity to jump from your project to your research plan. Hopefully the interesting elements of your project will feature in the stuff you're about to work on.
-- Second Suitor