I’m expecting Oda to do one of two things with Sanji and the RS
-have Queen able to temporarily disable it due to his knowledge of Judge, or more likely
-have Black Maria steal it, so Robin has to beat her and get it to Sanji, a la the need to beat CP9 to get the keys to Zoro/Usopp/Robin’s handcuffs.
Either way, I don’t think Sanji is swanning into the fight with Queen, armed with RS, Queen’s various plague completely neutralised from the beginning. I do very much expect to see base Sanji vs Queen, at least for a bit, with the RS being the thing that turns the tides, when he can finally use it.
We also notably don’t actually know that the RS can even deal with Queen’s plagues- we only expect it. It’s never actually been said in series that the RS can block infectious diseases- it being durable and fire resistant is what was hyped up. Does Queen, with his knowledge of the Vinsmokes, have a way to deal with raid suits? Who knows, but it certainly can’t be ruled out.
We have actually seen, three times in two chapters, Zoro being totally comfortable dealing with the fire of two characters vastly stronger than King. Zoro would have to be completely without his swords for a fight with King where King’s fire could actually play any role. He’d be as well being called King the Tornado or something in that situation, because his fire is irrelevant.
Unless Oda makes King’s magic fire different from BM and Kaido’s magic fire, there’s very little reason to see Zoro fight it. And I’m not really seeing a situation where we have Zoro cutting BM and Kaido’s fire, King having somehow better fire that Zoro can’t cut, and him then needing to learn mid fight to cut a different kind of fire. That’s just... kinda dumb.