Been thinking about the boon more, and I keep coming back to the wish for positive change. Abelheim wished for it first, and Mathilde repeated his words to his grave as I recall. Kragg the Grim refined it. The world changes all the time, but he wishes to finally see
positive change.
Karak Eight Peaks may be the single largest, most impactful positive change worldwide if it works out. I would see it in the same ballpark as Magnus founding the Colleges of Magic. If it heralds a revival of the dwarven race, (not likely, but plausible) then it may be even more significant. I don't want to take away resources from that. In fact, if Mathilde happened to receive a similar boon from another group, I'm fairly certain that many would vote to spend it to help the dwarves. Some posters have already been arguing to spend speculative elven favour to mend their relationship.
I think it would be entirely in character for Mathilde to tell Belegar that the biggest favour she could receive would be for him to remain a force of careful, deliberate, and most importantly
positive change. The most important way he can do that is by ensuring the success of K8P, which will have so many consequences it seems ridiculous.
Basically, he should dedicate himself to the path already taken. Don't be radical for the sake of being radical, but don't exclude things just because the are not traditional. It should not obviously
cost him everything, but asking a King to dedicate his life to something is exactly the kind of favour I'd call transcendent.
She is a Grey wizard and a Ranald worshipper, a hidden library/shrine and a modest bust of herself will do. Let the god to the testing of future prospects.
A Grey Wizard/Ranald thing to do would be to hide Mathilde in various images. Dwarves crafters create a massive relief on a wall? Mathilde is hidden in the shadows. I half remember that some famous artists used to do stuff like that, and I think it would be amusing if there is a finding Waldo situation, where Mathilde's presence can be inferred in various artworks. A shadow somewhere that does not behave as it should. A greatsword with runes seen at the edge of a painting. A witch hunter hat in a crowd. Stuff like that.
Didn't Disney Land do something similar with hidden Mickey Mouse silhouettes everywhere?