I think it will take a lot of time before other crewmembers than luffy can use haki. Honestly, at the pace it's going, it will take years before even Luffy starts using it. He's being so damn thick about it...He's seen Rayleigh counter Kizaru, Sonia and Mari inhibate his df powers, he's heard the kuja talking about haki, smoker too, seen logias getting harmed(even if only slightly) in the war and I'm not mentioning all the cases he's been in "contact" with this power. It's about time he connects the dots no? I know saving Ace takes priority in his mind, but still...he must realize that he's not strong enough...So he must ask himself "how do I get stronger"? And if he can't figure it out by himself, why not ask strong people around him? He's had three bursts (motobaro, amazon lily, wolves in ID), but has never thought of asking "hey, what's with me making people faint without touching them?", and never asked himself "hey couldn't it be the same thing Rayleigh has done in the auction room?"
I know it's no use complaining, but it's getting really annoying