These are only facts that come straight from JK Rowling in the recent Q&A online
By the time the series is done, we will know all the background information we could possibly need.
There will be a new Minister of Magic!
Poor Winky will never be cured of her Butterbeer addiction.
After the series is done, JKR plans on revising all seven books.
There was a reason that Sirius died.
Really bad things are in store for Harry.
Harry will continue to become more powerful as a wizard.
We'll see Moaning Myrtle again.
Harry's and Lily's eye color is important.
In book six we'll find out what Wormtail's been up to.
Crookshanks is part kneazle (I think I spelled that correctly...?). Check Magical Beasts and Where to Find Them for more info.
We will see Krum again, but not for a while.
Will Draco and Hermione end up together? NO!
We will find out what Dudley saw when the dementors attacked in book 5.
Right at the beginning, when Voldermort tried to kill Harry, how did Voldermort and Harry both survive?
JK Rowling replies -> That is the crucial and central question and if I answered it there would be hardly any point writing books six and seven... so I won't!
We will see more of Narcissa Malfoy.
We will also see Tonks again (yay

).
In the next book we will find out more about the circumstances of Voldemort's birth.
The muggle and magical worlds will not be rejoined.
In book six, the wizarding world is really at war again and Harry has to master his own feelings to make himself useful.
Harry will not be too busy for a little romance, however (but not Cho).
We'll find out what happened to Sirius's flying motorcycle (though it is possible to guess from what we already know).
¿will Harry and Hermione will be together?*sigh*
JK Rowling replies -> lol Not saying... but you've had enough clues by now, surely?!