OK, here's a thought. While I want to say that Dimitrov is going to pull off a victory that we'll look back on as a changing in the balance of power - sort of like the 2008 Wimbledon was, Roger passing (unwillingly) the baton to Rafa - I just wouldn't place my money on it. I don't think Grigor is quite ready to take Rafa. That said, I think he's going to learn from his probable loss to Rafa, and that the fire will be lit under him. Being in a QF is being a contender; he'll have been close enough to the Finals to smell blood, and next time around he'll really want it. We're going to look back at the 2014 as the tournament that Grigor Dimitrov arrived, and he's going to be playing into the second week at most Slams going forward.
Plus, I like his confidence, even if it is a bit premature:
http://www.tennis.com/pro-game/2014/01/dimitrov-playing-nadal-i-my-chances/50363/#.Ut8NJbQo4l0
I said it last year, but I think 2014 is the year we start to see not only cracks in the Big Four, like we did last year with Roger's fall, but in the Big Three. Andy will be wobbly for at least part of the year, Novak and even Rafa will prove to be mortal. Between the three of them they might still take all four Slams, but we'll start seeing upsets, leading to a true tidal shift in 2015, with 2016 being the new era. So it might not be the AO, but King Rafa is going to be taken down by one of these young pups this year.