Sasuke never intended to give Oro his body if he could kill Itachi that way.
That's obvious now.
He was just saying that to break the bond with Naruto and Sakura or to give Oro that impression.
Someone as obsessed with revenge would never be happy with giving up his body.
Because it would just be his body that kills Itachi, and not Sasuke himself.
He could watch Oro kill Itachi from inside Oro's mind, but that wouldn't be the same as killing Itachi himself.
And Oro would probably mumble some wierd stuff (like Oro does), laugh crazy or lick his face. Not satisfying at all for Sasuke.
Using the curse seal and slowly losing his free will or taking drugs to get strong is one thing, but giving up his body....never.
"For Feanor was made the mightiest in all parts of body and mind, in valour, in endurance, in beauty, in understanding, in skill, in strength and subtlety alike, of all the Children of Illuvatar, and a bright flame was in him"