It appears the Quidditch Tryouts will be included in HBP, based on Devon Murray's (Seamus) comments.
Devon says that he's hardly in Half-Blood Prince, but still has a bit of fun (says Seamus is the stupidest wizard in all of Hogwarts, in his opinion); there might be some pyromania with his character and he mentions Seamus trying out for Quidditch trials in the sixth film and doing a bad job at flying.
Tryouts were confirmed by an official picture.
McClaggen’s presence at the tryouts has been confirmed by him being in a calendar picture of Ron on a broomstick during tryouts.
The ABC sneak peeks showed more shots of the tryouts.
A shot of Hermione watching the tryouts came from the Behind the Scenes Featurette shown in February.
Melanie Slade, who can be seen also in the above shot, talked briefly about her small role in the film.
I was in a scene with Hermione watching a Quidditch game and had a couple of lines to say.