People complaining about the lack of main couple development when... uh... they basically promised to marry each other, and I think that's kinda about as much as you're gonna get? Of course, we do get some stuff like the end of last volume where Hori was struggling to outright state she liked Miyamura, plainly and clearly. She's still dealing with embarrassment over the relationship, which explains why she's still had some violent reactions even since the proposal. Tsun will tsun, after all. They're emotionally vulnerable like that, you know.
But, still... they really don't need more. The vast majority of the manga is slice of life and focusing on developing everyone. Decent gags and progress across the board is fine. There really isn't much more room to advance the title couple.