I personally think that if Luffy gets any increase, it'll probably result in him losing his bounty. I mean, we haven't see Whitebeards, Shanks, Kaidos, Dragons, etc bounty, probably because they're so strong that it'd be impossible for anyone (even for an Admiral and a fleet of Vice Admirals) to take them down to claim it. Proof is Gol D. Roger giving himself up, but the Marines claimed they captured him to save face, instead of telling the world that a dying man gave himself up just for fun.
But I highly doubt Luffy will get such a large increase, I mean, as people stated, he hasn't done all that much in the last few arcs. Escaped Impel Down with help (Shiki escaped alone, and without help), fighting in the war against the World Government alongside Whitebeards crew (and promptly got his ass handed to him in every actual fight), and that's ultimately all that he's done. Now, he DID punch out Garp (even though he threw that fight), so he could get a bounty increase, and he was unveiled as Dragon's son, but all in all, he's done nothing of note besides punching out Garp, so I highly doubt he'll get much of an increase, if at all.