I really do think this would be fascinating. Personally, I think this would cause a rift between Vernon and Petunia. Petunia was jealous of Lily and afraid of her, but she definitely doted on her son. I think if he'd been a wizard, she would have fought it at first but ultimately accepted it, whereas Vernon would still be very much against anything weird or abnormal to his mind. I think they'd split up, and Petunia would also warm up to Harry a lot more. There are hints of her being a better person than her bitterness and jealousy allowed her to be in the books; I think Dudley being a wizard would have opened her up to her better nature.

As for Dudley, I also think he'd be a Hufflepuff, and he'd probably have been a hell of a lot nicer a hell of a lot earlier - particularly if removed from the presence of Vernon.

Green Queen//Gryffindor//1