Sera is a bit of an airhead and spends most of her focus on art, but Ruriko had the patience to indulge her friend and wait a whole 5 years (one fifth of her life up to that point) to proceed with the plan, now they are married, she has ample chance to build up. I believe in her.
We thought Pengin was pushing progress at rocket speed due to her singlemindedness, but actually it was her pent up feelings as she has been staying by Shishimaru's side and watching her all this time. So sweet.
Well well, the classic literature reference game is confirmed to be received and surreptitiously reciprocated, at last. Konatsu, please continue "push push", I'm sure senpai will definitely "push push push" back.
I mean, one of the most important plot points in the story was the thing with Ookuma's parents, who were super conservative and super strict and forced all sorts of stupid rules on her -- like not allowing her to date anyone unless they explicitly give the relationship their okay! And for that the dating candidate would have to submit a résumé, have an interview with them, convince them that there were serious feelings involved, etc. etc.
There's no way the author would leave those issues unaddressed, unless the publishing company told her to end the series now.
I don't think this one is axed. The main story with the main couple has reached a reasonable conclusion at a kind of natural pace. Ookuma is starting to break away from her parents' protectiveness, that's a good start, but diving further into the family matters would require a diversion from the tone of the series so far, so I think it's okay to leave it out if the non-repetitive fluffs might potentially run lower than needed to buffer the drama. Using a fine point in plot like this to end the story on a high note is a good and safe option, imo.
As for the yaoi plot line with Kanda's brother, it's might potentially mirror the story of Kanda and Ookuma or whatever, but I suppose is along the old narration style "but that's the story for another day".
(May I suggest a story that kind of has similar premise at that point? I recommend "Natsuki-kun wa Kyou mo Kirei", involving crossdressing and onesided gay feeling since the crossdresser guy is straight.)