Damn.
Why should it end with them becoming a couple. Damn, getting together with your soulmate is usually the beginning for people, not the end... but it's a pattern that we've seen again and again, with the fucked up phrase "and they lived happily ever after" putting an end to the story when the main couple gets together.
But the power dynamic is still unchanged, and they're both really stubborn.
I think it would be fun to watch them trying to find their places and limits within the couple.
Also, a future where they're both is in charge of Kaguya's empire, with Miyuki trying to deal with the fact that it's still HER empire, and Kaguya trying to maintain dominance and a noble attitude while being worried sick by his situation. And the worries both of them would have about having kids, but no time at all to care for them, and not wanting them to be raised by maids...
What I kinda would like to see is a short time jump, when Miyuki comes back from Stanford, and meets up with her again. So much shenanigans could happen with that.