First vote of the quest is both the most popular of all time and closer than Brexit... Welp! Hope that those of us who voted for Sith Rionnasc stick around - sure we can still get a thoroughly intriguing (pun intended) museum out of this!
To that end... When considering the substance of the quest, I would argue that the most important quality in our curator is that they be a subject expert of some variety - in a matter other than piracy. That makes it far easier for tension to arise between the intellectual integrity and pride of the curator and what is politically expedient for our patron(s).
As such, I'd probably be least keen on Retired Pirate but just about anything else could work well - the Druchii's bending of their society into a war machine results in a variety of specialisations, Skaven have all sorts of bizarre competencies and, as Divided Loyalties has shown, it isn't difficult to combine magic with learnedness (or at least inheritance of a tradition of knowledge). That said, it's Norscan Sage that sounds most interesting, with potential to inhabit someone with knowledge and perspectives far removed from anything in the rest of the world*, even if I worry that people will be drawn away from it towards the most obviously unusual.
*Granted, Skaven Revenant also offers this but DL already does a fairly extensive examination of that culture!