@Jackermeister:
I think it would have to happen in the next arc, or at least at the end of it. They're already halfway there. If he eats it just before they reach Raftel or something, he would suck with it. Considering how long it has took for other characters to master their fruits, he needs some time to train.
Alright, in that case:
An argument I'm not sure I've seen brought up, although perhaps I've just missed it, is to look at this from the point of view of One Piece as being a story that is being intentionally crafted, rather than simply events that are unfolding.
From the latter perspective, sure, a situation where Sanji ends up completely outclassed in a fight and feels forced to eat the fruit in order to gain victory for Luffy seems feasible enough, and not even necessarily out of character; after all, we already have had scenes of Zoro being willing to give up his life, his dream, and his pride for Luffy's sake, so I see no reason why the same couldn't apply to Sanji.
From the meta point of view, however, the question you have to ask is, why would Oda have Sanji, or any of the Straw Hats for that matter, eat the fruit? Frankly, the obvious, and to me only, answer is in order to give that character a power up.
You say you believe it would happen in this next arc, or at the very least soon. So what you are saying is that Oda would have had the two year time skip, specifically so that the Straw Hats would be stronger. He would then proceed to have a few arcs post skip where the Straw Hats are essentially not challenged in the least, and stream roll their opponents, while seemingly showing off only the barest hints of the new strength they have gained in the process. Then, suddenly, within the very next arc, the difficulty would ramp up to the point that a Straw Hat would suddenly need yet another power up to succeed?
Everyone is entitled to their own opinion, as always, it goes without saying. But does that not strike you as just the slightest bit absurd sounding, from a story telling perspective?