Gilderoy lockharte; He was the prince but accidently erased his own memmory, before he tried it on harry andf ron in CoS, so he became a writer.
Colin creavely, yeah why not?
Seamus, a woefully underused charecter, I think he could be it, we know for sure he is half blood.
Here's my theory abouthow Jk should wind the series up. Harry destroys Voldemort by using a time turner and talking Tom riddle out of becoming voldemort. therefore Voldemort never existed and so is destroyed. Tom riddle becomes a fine upstanding citizen and manages florish and blotts in diagon alley, Harry's parents are alive and he grows up a normal kid who goes to hogwarts, but not famous, All the other dead ones, (sirius, diggory, numerous arouras) never died. and harry live happily ever after with cho chang?