As far as the narrative goes, Kageyama vs. Hinata as professionals, particularly if Hinata's team wins, would close out a certain arc that started from the very beginning of the manga. I'm actually a little worried that manga might end after this. 😳 Because otherwise, what happens next? Considering Kageyama, having played on Team Japan for Olympics, is already at the top of Japanese volleyball more or less, and transitive property of winning means if Hinata wins then he's clearly up there too, so can it be as interesting to follow the professional careers when the stakes are not like where in high school if you lose once (or twice if your third years are stubborn) the team you're on basically dissolves? We're seeing a lot of the key characters already (biggest omission in the immediate present is Oikawa, I guess), too....
EDIT: Well, I read somewhere that manga is indeed ending this year. Sad, but it was an amazing run! Since it's like this the mangaka might as well have shown 2nd and 3rd year of high school too, but I can understand if he's getting bored of volleyball or whatever. (But why does DnA get to go on forever? Meh!)