@Monquito:
Since there is no way Oda could know OP was gonna be a success, and it was another manga subject to cancellation like every other manga, more likely Sabo wasn't planned.
He was planned, just not from the start. There was evidence that he was planned around Drum or Alabasta, like Ace's tattoo.
@Monquito:
But just as we have discuss it before, Mera Mera doesn't fit him very well, at least not in the "Fruits chose their owners way" Teach and Ace commented back at Banaro.
Oda's been trying to sell him as a Ace 2.0 instead of a new character with own particular df ability.
Different backstory, different fighting style, different goal…
And how exactly Mera Mera doesn't fit him? Impulsive personality, draconic-themed martial arts, burnt scar, blue outfit to complement the orange flames...