I seriously doubt Oda had planned haki all the way back then; I feel like that was more of when you stare an animal in the "white eye" or in the eye of the tiger if you will, but sure, it's possible that Oda had some sort of haki planned all the way back then. There are also theories that Zoro learned haki during his battle in Alabasta (which is also like the last time since Zoro pushed himself to the absolute limit, except for the annihilation of Kuma), but some think not. Either way, haki began to get more serious with Enel, Rayleigh and Hancock, but not the kind of haki that makes you turn black and deal insane damage. That kind of haki was iirc never even seen before the timeskip. And now it just seems really common. Like everyone just automatically learned it.