I would like to do a Harry Potter RP but I'm afraid of the same thing; that it won't get anywhere.

But~
I could help with creating the world if you need someone to work with you cooperatively. I'm great at world-building!
I think the reason a lot of these RP's die is because they're not entirely original.

Here's a few ideas I have with a Harry Potter RP:
Plot;
 - evil wizard, enough said, makes weird things happen and people die at the school

Not in Hogwarts, which is based out of England/UK; how about somewhere else in the world? Even though it will primarily used to [i]start[/i] with, the grounds themselves can be incredibly different.
 - Netherlands
 - France
 - Germany
 - Switzerland
 - Italy
 - Brazil
 - New-Age school of Wizardry in the USA

After school things in order to give the RP flavor overall, even if they're not used directly, their places can be;
 - Magic Art, Dancing, etc. rooms
 - 1x1 Fighting and various places to train,
   + things to train with; giant stone armor, wild / enchanted plants 

Cast of characters, even if some are rarely used
 - not simply replacements of original HP characters, but new characters just as complex

Mess it up and throw in a few races that are likely to be in a fantasy world, I would probably shy away from frequent Vampires though. And all player's main characters as humans (or very close to it) attending the school.