i think oda shows us clearly that reaching after the PK-title could make you easily reach rock bottom.
so far luffys adventure wasn
t easy at all, but the SHs always managed to overcome those situations and had a reason to party in the end.
now, right before the new world, we see how those dreams could be easily crushed by those forces of the OP world..
luffy lost part after part of everything he ever saw as valueable!
first his crew..all his nakamas right before his eyes..
luffy was unable to do a thing..he was helpless.
than he heard about his brother and nearly lost his life on the way.(we can be sure that those poisoning and hormon injections will take massive effects on him in the future..)
luffy was always the type who sacrifced his own life to achieve something..but this time he sacrfificed so much for nothing!!!
in the end he lost his brother right before his eyes..
here was the point that luffy couldn´t anymore get a hold of himself..
it finally broke and crushed him.
now on top of that all, he lost his strawhat which always symbolized his dream to become PK and his bond with shanks.
i think oda shows us that luffy has again to stand up on his own, now that he lost everything so far and when he gets back his SH symbolises that he again has the will to reach for the top.
not giving up, even when he has nearly to start from zero.
in my opinion he will get back his SH when he is back from his emo-phase..
when he can gather a new spirit which will give him new powers.
overcoming such huge failures is sure one of the task you have master to be worth the title of PK..
achieving freedom is always connected with understanding how much that freedom is worth..and i think luffy is learning this right now.
also it will have the effect that luffy grows so that he can stand against future problems.