I liked the elemental scene heating up, but I think that one might need more prep, and it's not completely global.
And Peter's still too young to be the next dark lord

I think it'd be interesting to see a new type of supremacy crop up though. Prejudices against purebloods could be a really interesting idea.
I do like the inter-school idea. It'll give some of the students who have less plots a chance to get rejuvenated.
Rogue magical creatures? Some sort of disgruntlement with the wizarding government somewhere with like, the centaurs or mermen or giants. Um, some random little country deciding it hates everything else (WWIII wizarding style >>). New families trying to assert power now that some influential families have been busted due to dark associations. Uh, discovery of a really weird new potion or creature or ingredient or spell that goes wrong or becomes a big hit.
Instead of the triwizard tournament thing, have like teams? Conceivably every student could be on a different team specializing in something.