My earlier misgivings turned out to be unfounded as very little focus is granted to the blonde girl in these four novels. Honestly… very little of anything gets any focus since not much of note occurs in them.
The northern princess is still in concubine limbo, his wife remains dead-set on making him take more concubines (the blonde girl still waiting in the wings), and there aren’t any developments to speak of besides some rather strong indications that the series wants to develop into a war drama of all things. The thirteenth book ~might~ finally result in the princess becoming an official concubine, but with the way things have gone recently I don’t trust the author not to drag it out further with church-related shenanigans.