Tbh I dont really think much of the rival thing anymore. Like
@Fujishiro said, its probably just him helping and guiding Luffy.
It was already implied at the end of Wano that he seemingly knew either Luffy or Ace were destined to eat the fruit. Im like 90% sure he was in Windmill to see Ace, given who Roger is to Shanks. Luffy eating it probably was the only surprise. He expected Roger's lineage to carry that destiny.
And evidently he waited this entire time for the fruit to awaken itself, especially given his reaction he didnt start "moving" until that point.
I think whatever "hype" we have attributed to Luffy fighting Shanks can just be transferred over to Shamrock. While Id like to see it, Im not expecting it given this. If Oda actually still gives them a legitimate fight for legitimate reaspons I would be absolutely shocked lol