Nearly forgot to vote
Quite a range of options to choose from. Thought I'd do a rough analysis for them as well. Mostly speculation.
[X] The Waystone Project
A project that will be very difficult, long and has massive implications in the long run for the world. In addition Mathilde will have to get Dwarves and Elves to work together, and manage the Colleges contribution as well. Heavy research focus along with going out to visit lost or broken waystones, I think. Lots of potential for travel.
[X] Loremaster-at-Large of Karak Eight Peaks
As several others have said, this is basically the job we're doing except on wider scale. Unusual solutions to unusual problems, probably via magic sword.
[X] Border Princess of the Howling River
Next door to K8P, Barak Varr and KaK. Easily reinforced from any of them. Barak Varr will probably be supplying materiel and troops, either their own or mercenaries, and I can see Belegar matching that support. The Winter Wolves are likely available as well, going by the recent updates concerning them. Civ building near friends and allies.
[X] Governor-General of Swamp Town
Mystery box option! Thought it was a bit random till I looked at the
wiki and saw it was founded by a group of gamblers. Secret Ranald settlement, perhaps? Based in Lustria so it is very far away, very close to Lizardmen and Slann, not far from the Vampire Coast and sounds like a place Nurgle would love to visit for a holiday. Still, it is a mystery box and I'm always on board for anything to do with the Lizardmen.
[X] Ranaldian High Priest of Kislev
Spread the worship of Ranald, find out more on the Kislevite Gods and Ranald's connection with them. Further the relationship with the Ice Witches and other groups in Kislev. Visit Karak Vlag and there might be opportunities to go on expeditions into Norsca to find out the fate of the Norse Dwarfs. Or it might be solely focused on Kislev and its immediate borders.
[X] Ambassador-at-Large to the Karaz Ankor
Likely to be similar to the Loremaster option, only diplomacy focused and having to deal with groups of bickering people, and reporting directly to the Imperial government. Would rather be Loremaster, but I'm interested in further details.
[ ] Markgraf of Eastern Stirland
[ ] Count of Sylvania
These options will mostly be building up the infrastructure of Sylvania and ensuring the Vampires, and other things, don't ruin all the progress made. Likely to be options to help Kasmir as he attempts to revive the worship of the old Gods of Stirland and Sylvania, which does sound interesting, to be fair. Overall, though, I don't mind popping in to say hi to friends and check on the recent adventures of the sheep in the fief. Maybe whack the odd gribbly that appears, if needed. Otherwise, I'm happy leaving Stirland and Sylvania to Roswita. She seems to be doing ok.
[ ] Spymaster of Wissenland
Been their and done that. I mean, skaven fighting is fun, also lots of opportunity to loot everything that isn't nailed down, but I have to say I haven't got much interest in working in the Empire at the moment. Plenty of other places to loot, as well. Also, the Count didn't leave a very positive impression from his attempt at taking out the skaven under Nuln.
[ ] Bodyguard and Tutor to Prince Mandred
Doesn't sound that interesting to be honest. I mean, lots of opportunity for intrigue and finding out the goals of Heidi and the inner politics of the Empire. Maybe sent on heists as well to various places in Altdorf by Heidi. Unravelling spy rings and stopping assassination attempts on the Prince. Digging up dirt for Heidi to further her and Ranald's goals. Personally I'd rather sit in tower at K8P's and research stuff.