Luffy has already clashed several times with Kizaru so it's totally alright if he gets a clash with Saturn, he hasn't even acknowledged yet that Saturn is on the island. That will happen next chapter.
Apart from that I believe Luffy vs Kizaru round 2 is the extremely likely matchup. The easiest arguments I can give you are:
- Volume cover
- Luffy and Saturn simply aren't compatible for combat. That's how easy it can be.
Main reason why I think Luffy vs Saturn won't be a full 1v1 fight is probably Bonney, Kuma and the ancient robot. The ancient robot went to the holy land 200 years ago but ran out of fuel before it could do anything. Clearly it went after CD and coincidentally we have a leader of the CD on this island. Funny enough Kuma has done unprecedented damage to the holy land just earlier this arc.
Bonney transforming herself or Kuma into Nika using distorted future is also most definitely going to happen. Saturn was actually dissapointed in Bonney that she didn't make the connection, probably because as a scientist he wants to see the full potential of Bonney's fruit since he gave it to her. Coincidentally VP uses the same words this chapter saying that now Bonney has made the connection which essentially means she can turn into Nika.
I'm not saying Saturn will lose to them but these confrontations need to happen. Kizaru is simply a bodyguard, that's his sole role for the arc. He already let Kuma and the crew attack Saturn, but he definitely cannot allow Nika to attack Saturn.