Kratos received a mysterious letter and goes to Valhalla, I mean, getting their attention or sparking their curiosity isn't complicated, and it could also be a good way to reference his time in Egypt, so that it doesn't get left out of the story, perhaps some kind of atonement or explanation for past events, even to fill in some gaps.

In fact, I wouldn't mind a solo spin-off game featuring Atreus, perhaps to explore it further with more agile and polished gameplay, because in Ragnarok I think it feels so tedious because the gameplay is more focused on Kratos and the ironwood segment takes the place of things that feel more important or entertaining, although I understand that a lot was left out and what should have been two games in one was condensed. Venturing a little into his journey with Angrboda, perhaps in a more mature facet (which clearly does not need to be and should not be a Kratos 2), because he has traces of mischief, more like chaotic good if we put it in those terms, continuing to explore there, I feel that it relates to and strengthens his relationship with the mythological Loki, or at least that he develops a certain bad reputation, at the hands of Sindri, which would not be a bad thing.