Great question.  I'll say a few things (but others may have different takes).  One, it's always safe to be gung-ho/enthusiastic about what the firm does and about the prospects of staying.  Firms are making a serious investment in you, and--beyond that--the people who are truly interested in making a run at partner are more likely to put their best foot forward (i.e., do better work).  So why wouldn't an interview select for those types?  That said, I'll also say that I think authenticity is critically important to a great interview.  And I was always deeply skeptical of candidates who were a little too excited about the job because--in the main--most law students really have no idea what they'll be doing at a large law firm.  So I, personally, believe a middle path is best.  Try your best to express genuine, open-minded interest in what the firm does and making your best possible contribution to it, while also--if it happens to come up--feeling free to express your commitment to pro bono and public service and your desire to explore the best way to serve moving forward.  I'd stop short of indicating that that's your "plan".  But there's certainly no reason you can't express that it's important to you and that you're doing your best to explore all your options so you can make the best decisions.  That rings true for most people, and it'll be the rare interviewer that'll hold that against you.  Make sense?  (For a great, related discussion from the actual podcast, give it listen:  https://blacklinesandbillables.com/associate-success-and-development/ep-4-panel-callback-interview-qa/)