They might have an epic celebration. The Straw Hats would be excited to see Shanks, especially Luffy. Luffy would probably challenge Shanks to a friendly duel or just be overjoyed to show him how far he's come. Shanks would be proud of Luffy and his crew, and they could all share stories of their adventures over a big feast.
They might have an epic battle to test Luffy's growth. Shanks could see how much stronger Luffy has become and be proud. Maybe Luffy will show off his new Haki abilities.
A cool plot would be when the Whitebeard Pirates meet Luffy while he's on a quest to find a rare Devil Fruit. They too are interested in that Devil Fruit for some reason. Instead of fighting over it, they decide to team up. Luffy's unique perspective and the Whitebeard Pirates' experience combine to create an epic journey filled with challenges and new discoveries.
In fanfiction, when the Whitebeard Pirates meet Luffy, they might initially be cautious. Luffy's reputation as a rising star in the pirate world could make them curious. Maybe they would test his strength. For example, some might engage in a friendly sparring match with him to see what he's made of.
In the fanfiction, when the Whitebeard Pirates meet Sabo, there could be a show of strength on both sides at first. However, Sabo's connection to Luffy might make the Whitebeard Pirates more friendly towards him. Ace was part of the Whitebeard Pirates, and since Sabo was like a brother to Ace, they could end up having a big celebration in honor of Ace's memory, with Sabo learning more about his time with the pirates.
Well, it might involve Shanks sharing some valuable wisdom or revealing some secrets about the past. There could also be exciting battles or adventures as they face new challenges together.
Luffy might be more confident and less like a little kid around Shanks. He has grown a lot, and Shanks would notice this. Their relationship could become more of an equal partnership in terms of respect.