I think it's pretty common in Japan to arrange marriages, even more if you can make good business or productive connections. I see shinomia having an engagement coming to her. That's why kei's words felt important, because she was treated as shinomia in that regard, so she escaped. An eloping arc could be on our way, or something that drives them apart.
On the other hand, shinomia could have done something bad (not on purpose) by contacting shirogane's mom somehow. I'm sure the mom is successful and when she find out how brilliant her son has become, she'll try to take him away (on the other hand she could come after kei and give him the cold shoulder).
I think my point at the end of the day will be like the ancient Japanese story, where shinomia will inevitably get separated from him because their differences in social status. But after a long route he'll find her wherever she is because of his determination (at least I hope so)
It would really feel bad or bitter sweet to see them separated, something like shinomia in her empire watching pictures of her and shirogane and then a cameo of a trash can with a wedding invitation of shirogane and Fujiwara (XD) and then a single tear runs down an emotionless face (uff).
I got a little carried away he he.