It is something I've guessed yeah. I think Kizaru could be the next logical step for Luffy, primarily because of his power. Luffy's fights are rarely ever cerebral, it's best to leave the braniac type fights to other characters. But Kizaru could be really fascinating here, and defeating him now is objectively fine because you still have Akainu, Fujitora and Ryokugyu for Luffy, Zoro and Sanji if needed.
Its similar to how Luffy defeated Katakuri then Zoro/Sanji defeated YCs the following arc. Maybe Oda wants Luffy to defeat an Admiral before these 2 would. Plus Kizaru and Luffy have had some decent beef beforehand lol. If Kuma returns to this island, I vote Zoro fighting him somehow, simply because his power is super fucking broken too lol