My reasons, for Markgraf have been already been outlined by other, but I'll reiterate them in my own words anyway.
I want to close the circle and return to the roots of this quest.
After Abelheim's death, Mathilde was pretty much exiled from Stirland. Not literally, of course, but between the constant reminder of Abelheim's death, and the anger at Roswita's bigotry and the failures of Sigmar she couldn't stay there.
So she left. At first to the Colleges, and later to the Dwarves.
At this point Mathilde was no longer the plucky and naive Apprentice-turned-Journeyman that first arrived at the Witchhunter's Court.
She was now a fully fledged Magister and ready to show the world what she can do.
With the Dwarves, Mathilde grew. Both in character, in strength and in wisdom. But in many aspects, she never really managed to address her scars. The dwarves can be stubborn and inflexible, but they are also generally a people of integrity and honor. The foes she faced were the enemies of civilization. The line between good and evil clearly demarcated. A classical tale of a hero saving the world from evil.
I couldn't find it right now, but I remember there being a conversation between Abelheim and Mathilde about making the world a better place. Back then the world said No and threw her words back at Mathilde's face and left Abelheim a lifeless corpse. She managed to salvage the campaign and even raze Castle Drakenhof, but between Abelheim's death and Roswita expelling her, this was a bitter victory indeed. Heroic deeds managing to defy impossible odds, yet even so the world continues to turn on its cruel trajectory.
Now I want her to return. Last time Mathilde might have had to bow down before the realities of the world, but last time she was also a mere journeywoman. Now she's coming back as an accomplished Lady Magister of the Grey Order, one of the very Blades of Judgement that guard the Empire. I want her to to walk in there, into the very place that spurned her so long ago, and declare that she will make Abelheim and her dreams come true.
And this time, when the world comes to stop her, she will be the one to say "No! Fuck you!" and force her will upon the world.
I want Mathilde to boink the Sylvanians over the head and make them get that Daddy Carstein ain't around anymore!
I want the Dämmerlichtreiter to once trott down the roads of Stirland, finally coming to dispense justice to the wickedness that has taken roost for so long in Sylvania!
I want her to show up the Sigmarites, and demonstrate how not to be an incompetent fuck-up and successfully integrate a province into the Empire, making the Sigmarites either step up their game and show their worth or prove once and for all - for all to see - that they and their god are all bluster and no substance. A restart of the character arc revolving around Mathilde's Distain for Sigmar, that was unfortunately cut short before it even took off due to us running off with the dwarves.
I want for Mathilde to close the circle and step up to take Abelheim's place.
Just like this story commenced with a shy Mathilde creeping around the entrance hall, before The Elector Count demanded the full attention of scene with his mere presence, I want The Dämmerlichtreiter to be the introduction to a plucky advisor's tale of how they will shape the world.
Let's go full circle
So, once again with feeling.
[X] Markgraf of Eastern Stirland
[X] Bodyguard and Tutor to Prince Mandred