The second option with Luffy vs Kizaru is the more likely scenario, there is no way Oda isn't going to have Luffy not fight an Admiral.
Having Luffy fight Kizaru is Oda's way of showing how strong Luffy is compared to an Admiral now, and I know many Zoro and Sanji fans might not like this but they might either fight the Seraphims or the Vice Admirals.
The big question though is, will Oda have Luffy defeat Kizaru.