To be honest its still way too early to make an accurate prediction as to who will actually end up eating the Mera Mera no Mi, if someone eats it at all.
However it couldn't really be more clear cut that Sanji will not be the one to do so.
Oda would not spend the vast majority of the manga building and improving upon the black leg style only to make it irrelevant with him eating a logia devil fruit, especially one that we associate so much with Ace.
Seemingly basing it on a real life fighting style in capoeira, making his mentor Zeff use the precursor to it and pass it on, design and name attacks to fit in with Sanji's theme as the ship's cook, bring in a major upgrade like Diable Jambe, have him train with that fighting style over the two year timeskip, think of new ways to expand upon it with blue walk, sky walk and hell memories. That's not even taking into account that we still haven't the limit of Sanji's strength and techniques pre-timeskip by a long shot.
Oda does not build and then demolish for no reason, and Sanji eating the Mera Mera would be an excellent example of such, hence, despite the compelling argument that "Sanji could light his own cigarettes", it will not be happening.