First off.. Luna has a thing for Ron, not Harry, if you can't tell. And she's stopping at the 7th book, so wtf would it show Harry as the headmaster and Hermione as a teacher and shit? It's quite obvious Harry is going to be an auror if he lives, however, I have a feeling that
A. Voldemort kills Harry, Dumbledore kills Voldemort.
or
B. Voldemort kills Dumbledore, and Harry kills Voldemort.
And, Luna does not seem to have that powerful of magic.. I think Neville is getting much better and will do something important though, such as kill the Lestranges for torturing his parents or something similiar. Luna will be an important part, as she was one of their new "friends" and stuff. Yea.
I also do not believe Sirius is "dead," as he was hit with a RED JET of sparks (Avada Kedavra is green), and he vanished behind the veil so they will not know if he died or not. Also, I think when another person dies who is close to Harry, they will become a ghost and stuff.. >.>
@Sek- True, Sirius was not a MAJOR character, but he was becoming one. I would have rather had Arthur Weasley die, but that's just me.
About Grawp, I don't think he is going to persuade other giants to join Dumbledore, as he's around 16 feet tall. I think Hagrid is going to find him a wife, and they are going to live in the Forbidden Forest and "breed" giants to fight for their cause, or take over the other Giant tribe, or something.. Yea, I don't remember all that was said so far, but I tried to reply to all the major things.