User blog comment:The Koromo/Chapter 758 Review: Again/@comment-4493594-20140828204202/@comment-4899461-20140829140810

You could make the argument that Haki's useful for everyone, since it would just be a refinement on abilities they already had. We've actually kind of seen that with the members who do have it already. Such as Zoro vs. Mr. 1 kind of being Kenbunshoku, other having super-human senses of awareness, etc. So for example, Nami adding Kenbunshoku to her already astute sense of weather would be good. Robin having it to heighten her sense of where to spawn body parts would be a useful skill too.

And let's not forget one of the main attractions of Busoshoku: The ability to fuck up Logias. That would be extremely useful to someone like Chopper, who can't use seastone because of his own DF powers. I wouldn't be surprised if Franky and Chopper ended up with it, given their place as heavy-hitters in the crew.

As far as Brook, I don't see why he couldn't have Haki, as the tendency with his devil fruit seems to be that the connection to the soul is more important to the body.