Let's put it this way. Everyone's saying: "no, the SHs don't have haki, it wouldn't be cool, bla bla".
I wonder, why shouldn't all SHs have haki? Let's see the things here. The Kuja pirates, aren't the strongest crew in the world, and yet everyone has some kind of haki. It's said that everyone has the haki inside (the two types, without the CoC), so everyone can learn it.
SHs will probably be the new Pirate King crew. If we look at thhe whitebeards, Jozu and Marco used haki to fight (the first, and the the third mate. Also Ace could use haki as well, and I'm sure Vista is capable of that too). Whitebeards are one of the greatest crews there is, and the first 5 people, including Whitebeard could use haki.
Haki doesn't mean you're the strongest, but it can improve skills. So my guess is that every SH will have at least some kind of haki. Luffy has already those three, I wouldn't wonder if Zoro had the three too. Sanji the CoA nad CoO. Usopp could have the CoA to improve his weapons, just like Franky and Brook. Nami and Robin CoO, and Chopper CoA.
What do you think about this, but I expect good arguments.