In addition to more about Nishigawa I'd also wanna see what happened with Shirotani's father, he called the father, but it seems horribly unresolved.
True, I assume they're getting along but there wasn't much info about that. Honestly, Shirotani's story alone would have added some very interesting chapters.
"Volume 6 is coming out" is just the recollection of all the chapters that represent volume 6. In other words, it just mean they will sell the latest chapters joint in one "book". For example, from chapter 40 to chapter 48 (since they first sell it in unity in an issue/magazine, or the chapter itself) That's all
*means
It says "Volume 6" is coming out so... I'm confused. It just felt too open-ended for me, though that's better than a tragic ending. Contrary to what others think, I see them as lovers, it's just their relationship is still developing and Shirotani is still learning to express his own feelings. There is still so much unresolved, though... it would have been nice to have Kurose meet his old neighbor again so he could see how he impacted Kurose's life.