If electricity worked. No more lumos, I know, but also Arthur would be able to use a telephone, Hermione wouldn't have to patiently explain everything to Ron (OK, she would have to patiently explain LESS to Ron), no more pesky candles, PLUS central castle heating, and it's easier on the house elves.
If Slytherins were rasised in the evil baby orphanage. But then they might be raised so well, there wouldn't be Slytherin ... So,
If Slytherins were raised in the moderately and potentially unkind baby orphanage, that still leaves room for Slytherin antics, just no
If Muggles weren't so damn ignorant and foolish. This would avoid the 'Muggles are lowly and crap' mindset held by many evil, or potentially unkind people, and also would avoid the 'Muggles are silly little things. Like ponies. If ponies were silly little things' mindset of the rest of the wizard population. This would be world
If there was some kind of voting system for the Minister for Magic. Because I don't know how the hell he gets in, but if it's based on the Wizengamot, well, they all seem like a bunch of biased fools anyway. Excluding Dumbledore. He kicks fictional butt.
If there could be half/half houses. I personally relate strongly to the Gryffinclaws (I hope that's a thing), and I know a large number of Slytherpuffs. This, I feel, would reduce the emnity between house, and result in a far more confusing, yet far more harmonious Hogwarts life. Though Quidditch would be difficult ...
If the Slytherin common room wasn't so nasty! I mean seriously, I know they're badass and everything, but surely they wouldn't mind warm, comfy couches either? Just because they're cold-hearted, doesn't mean they want to be cold-toed.
If dementors were eradicated. Come on! How do you know they're not going to breed out of control, and -- wait, what?! DEMENTORS BREEDING? Ewwwwwww. Even ridiculous amounts of 'w's cannot aptly express the grossness of that concept. SEE? They need to be taken away! Scary, horny dementors.
If I thought about how much I freakin' want to go to Hogwarts a little bit less, perhaps maybe.
Eh. I'm cool with it.
Because I'm secretly Ebony Dark'ness Dementia Raven Way.