It depends. Imo we will have no admiral as a villain of an arc, also how can Kizaru be the villain of the arc when we just had Kaido and BM? And the way Oda presented it suggested this was side detail. If Oda intended Kizaru to be for real the villain of the arc he could have done again an intro for him like he did in Sabaody (a badass intro in other words and not a "oh, right, Kizaru is coming to egg head island too"). Actually now that I think about it there is also a chance, small, that Kizaru will backstab the CP0 since he, along with Sentomaru, was tasked to be with Vegapunk (also Sentomaru has just been stabbed by Lucci, who knows, maybe we will see an enraged Kizaru, this for once would be a nice twist, haven't seen one since Zou arc).
Anyway as things are right now the main villain seems to be Lucci, of a short arc, but probably with the next chapter the S series will start to attack the SHs... And we have seen with BB they are nothing to laugh at. There could be also nice match ups: Luffy can keep having Lucci. Zoro takes chibi Mihawk. Sanji or Jinbe get baby Jinbe while young Boa could be the enemy of Sanji (please Oda no), Jinbe (but I don't see the link) or even Nami.. this should be enough. But if you add an admiral too we should be close enough to an actual threat to the emperor SH crew. Also Luffy, even if he is fighting in GT vs Lucci doesn't seem serious yet, but Lucci on the other hand had the leisure to take down Sentomaru (but this can be sold too with Luffy being a moron).