Nah, I think Hinata (and Kageyama, too) does have enough ambition and motivation to be a Slytherin, but lacks other vital characteristics. And generally, I think they both just fit into Hufflepuff much much better (YES and Kageyama too).
When I first posted my headcanons for the sorting of Haikyuu!! kids many people wrote messages about not quite agreeing with my placement for Hinata and Kageyama. (I’m sorry I’ll be writing about Kageyama in this one too even though you didn’t ask, because I don’t feel like missing a chance):D Like, classically there goes Gryffindor for Hinata and Slytherin for Kageyama. (nah I like to think that he LOOKS like a Slytherin at the first glance, but once you get to know him better it’s obvious he belongs in Hufflepuff); Some of people who wrote me were even unsatisfied because for some reason they don’t like putting their main protagonists or other important characters in Hufflepuff. I have a question.
Why? What’s wrong with being a Hufflepuff?
Nothing.
So here we go. Both Hinata and Kageyama are hardworking as hell. As genius as Kageyama is, he still works his ass off perfecting his serves, tosses and receives. Hinata simply works as long as he can before actually throwing up or passing out. Hardworking? Hardworking. Point for Hufflepuff.
Then, in Hufflepuff’s description it’s said that the students of this house are loyal, patient and are often seeking friends. Which is my second point. Remember junior high Hinata? Hinata who didn’t have a setter to toss to him, Hinata who wanted true teammates so badly he was pumped to go and play for Karasuno’s team and find out what the setter of the team was so he’d finally have that setter-spiker bond. The reason of Hinata’s desperate need in a team was the reason I was persuaded he was a Hufflepuff. Then, a similar thing goes to Kageyama, because I think Kageyama is loyal enough to be there. He didn’t know what actual friendship/teamwork was in junior high, but once he learnt it he does everything to keep it. Everytime Hinata messes up or goes dejected? Kageyama is there to help in his own a little twisted way and reassure him. (as long as I’m here you’re invincible I mean c’moooon);Kageyama often yells at Hinata and sort of bursts out a lot, but then he is actually patient enough to stay by Hinata’s side even though Hinata sucks at so many things. Before their first match they practice receives for so long, and even though Hinata sucked back then, Kageyama still was (kageyema-patient) to actually keep going.
Also frankly, they both are kind of idiots when it comes to things other than volleyball, so considering brilliance comes from different ways for each of the houses I decided on Hufflepuff:D