If Oda wants Sanji to have haoshoku, he will. People arguing that he doesn't have the quality of a king are missing the point: Chinjao stated there are tons of conquerors in the New World and Sanji already is one of the strongest people in the whole world (just took Kaidou's top 2 after King, imagine by end of series), plus the fact that believing in All Blue and searching for it has a huge romantic weight that totally fits the spirit of the big dreamers in this series.
Most of you just overthink this. Sanji is one of the strongest people alive (not saying he's a top tier, of course, but he clearly is extraordinary and still didn't reach his fullest), he will be a top man of the Pirate King and he has one of the purest romance-driven dreams in this series. If Oda turns him into a conqueror it will make total sense.