Shanks- I don't know what to think about Shanks at this point. He's not shown much, but when he is, it's usually a big deal. He started Luffy on his quest to be a pirate, he tried to convince WB to keep Ace from chasing BB, he stopped the Marineford War, and most recently walks his smug ass into MarieJois with absolutely no fear.
Shanks is also depicted as being left-handed, and there are superstitions about left-handed people being evil. I think Shanks is going to turn against Luffy to gain the One Piece for himself. Or at least, that's how I would write it.
What if Shanks recognized that Luffy had inheritied Roger's will and realized that he was going to have to set things going for Luffy? He encourages him to be a pirate, and gives him Roger's hat. He also prompted Luffy to promise to bring it back to him.
I think Shanks has planned to use Luffy to get to Laugh Tale and to take the One Piece for himself.