It's too early to say if he'll qualify for Candidates, but he has been playing well so far, I agree.
Though, he hasn't faced his toughest opponent in this tournament yet: Levon Aronian.
Levon has a winning record against Hikaru, in Classical, so for Hikaru to win, he'll need to perform better than he has in the past ...
He has just defeated very strong GM Richard Rapport whose rating is around 30 points higher than Naka's. Hikaru made a relatively long break from classical chess and it seems that it did him good.
What do you think how far can he go? Is he going to qualify to the Candidate tournament? I definitely hope so, he is one of my favorite active players.