Luffy
Shanks
Rayleigh
Ace
Whitebeard
Doflaming
Hancock

are so far the only confirmed Haoshoku Haki users. And I think its safe to say Dragon, Garp and Roger fit into the list aswell.

My question is which characters will be shown to have this form of Haki in the future?
How big should the number of users go so that it is not yet ridiculous (like sharingan for example)?
Do you think there is more to it than knocking out weaklings seeing what an effect it had on the participants of hte MF war? if so, what?