I think its a major error to think of Shippuden as an entirely new series... because it isn't. o.o Part I is Part II's base. You simply can't discredit the first half of a novel, so to speak...
And the characters haven't changed that much... at least not in my opinion. They've all matured and grown stronger, but their personalities are still the same, the core of the characters has remained the same. Until Sakura openly states that her feelings have changed, until Naruto does so, and until Hinata does so, I will believe that the romantic feelings haven't altered in nature or of who they are directed towards.
All things considered, I think it will be the bonds that Naruto and Sakura offered to Sasuke at the end of Part I, that will save him. I don't think Kishi's intent is to change those feelings, instead, I believe he wants to preserve what he established in Part I and deepen it in Part II. That seems to be what is necessary for Naruto and Sakura to accomplish their goal.
And going with the themes of the series... bonds, people accepting other people, the next generation surpassing the former.... It's hard for me to imagine Naruto rejecting Hinata if she ever does confess to him... But, depending on how its handled, I could accept it.