I don't regret hyping up Sanji vs Kizaru, I'd rather have high expectations for Sanji then be let down again and again than have none and only get excited after he shows off. I'll take the L, Sanji has his position in the crew that allows Oda to be flexible about when to have him save the day or fall short, it's frustrating but it is what it is.
I would have said that there's a chance we get Kizaru as Sanji's Admiral opponent in the future, but Oda seems to be going all out character-wise for him here against Luffy, so I think Sanji will face Aramaki instead. Sometimes things just don't materialise the way you want, sucks. Sanji blocked a beam, got hit by one then got up (it ain't amazing, it ain't terrible, just underwhelming if you had big expectations like me). We'll see the dialogue and whether or not he was protecting others, but it doesn't change the situation much.
As for where Sanji goes from here, depends on how much hype Oda wants to give Luffy. He'll likely win Luffy vs Kizaru round 2 which I'm pumped for, but if Oda has the giant robot, that was already woken up by Luffy, do all the work against Saturn then I don't even know. I like Luffy, and his moveset in G5 is fun, but that sounds kinda excessive.
I'm actually happy to be wrong about Luffy vs Saturn, Kizaru's much more fitting for Luffy as far as his standing and position goes (he's a lot more well-rounded whilst being a top-tier and he's an Admiral, someone Luffy claimed he'd beat). Kizaru can be ruthless when he needs to be, I know it probably pains him, but he was clearly gonna axe Kuma and Bonney, he ain't a good guy, he's a conflicted man with a tough duty to uphold (similar to Aokiji except Kizaru understands his role as a needed component to a system that's flawed but keeps the peace). Luffy as someone without any restraints (at least initially before being someone's reincarnation) who follows his own beliefs and will through and through, facing him fits well.
Saturn only worked in my mind earlier as he could better warrant nika showing up due to all the pain he caused Kuma, but instead Oda had Kuma stand up for himself and pay him back, then had Luffy show himself as nika to Bonney against Kizaru. Now, perhaps Saturn will face the rest of the island. Kuma seems like he can move a bit, but I don't think he'll be sending Saturn flying again or anything that major. Sanji's still up and fine so maybe he'll aid a lot, it's just a matter of how much the Ancient Robot will do. I could see it defeating Saturn in the very end if Oda feels Kuma had his time to shine with his arrival.
Ultimately, everybody acts tough when they're up, it's having some faith in a guy that's disappointed plenty before that I'll continue doing. Oda didn't bring up Sanji's eyebrows in that SBS, tell fans to pay attention to him, hint at it a bit more with the S-Shark clash just to wait arcs to follow up (I hope), I'm going all in for Sanji playing an essential role against Saturn. I don't mind Luffy taking centre stage, this is a good match-up, just would've wished Sanji did more.