I've said it before, but Gaku is totally gonna be the captain when he's a third-year. In two days, he managed to turn Shou from a curmudgeon who thought of him as a nepobaby into a sworn brother.
I frankly don't know how the inter-high and the nationals will play out. Winning the inter-high seems narratively baked in - it confirms the Umino team's rapid progression under Kyogoku's baton, and it gives the third-years their moment of triumph over the local rivals and unsettled scores before they move on to college.
But nationals… the way I see it, if this is a short series that lasers into one year of the life of a volleyball team, and the rise of new star libero, then the denouement is Gaku's climatic victory in the finals against Hodaka, Noboru and his father.
However, if this is planned to be a full coming-of-age story, winning the nationals on their first run becomes less likely. It makes more sense for them to go to nationals and be defeated by Hodaka, or even another school, only for Gaku to have his revenge against his father postponed till the third year.
Of course, the author could choose an unorthodox route in which they win their first nationals, but then things get derailed from second year onwards, as things like the departure of the third-years and Aoi's poverty become issues. Maybe Umino will experience a slump and mature from the experience for a comeback in the third year. And let's not forget that given Gaku's goal to be the world's foremost libero, the story may even go into his adult life and career.
I'm really curious about Noboru. We won't see him again till nationals, I expect. Before that, Gaku will probably be pitched against Katase's team and deal with facing a friend and former teammate for the first time. But the thing with Noboru is personal because Gaku sees him as the embodiment of Kei's decision to discard his own son. One could argue that Noboru isn't to blame for the father-son feud and he was just embracing the opportunity to be trained by the best hitter of the previous generation. But I don't buy it. In my view, the moment Kei told him to keep their training a secret from Gaku, and he agreed, Noboru betrayed his teammate. He's the kind of chap who puts his own convenience above all other considerations.
I don't expect him to be some cartoon villain, though. He might apologise. Or it might turn out that Kei tricked him into keeping it a secret from the entire team for some trivial reason ("it will be a riot if they learn you're getting private lessons from me"). But I think Gaku has a right to be pissed about him.
By the way, one thing I like about Gaku is that while he's fully adversarial towards other teams, he doesn't see the players themselves as personal enemies, and shows good sportsmanship. With the supermarket bloke, the moment Gaku found out he was from Satta, the first thing he did wasn't an open display of hostility, but to ask what he thought of the Umino team. Only after the kid showed he has no respect or appreciation for the losers' fight did Gaku finish gauging his character and decide to throw down the gauntlet before leaving. Gaku is the kind of person one could trust to be a good friend, and a good judge of character.