In a flashback! Shiki is a canon character so he will be mentioned by other characters from the previous generation. But when it comes to him appearing right now in the current story, I highly doubt that that will happen. You see, usually they use characters in the movies if those characters don't have a big significance in the actual story. Here's what Oda said about Shiki in an interview...
Even before the movie, Shiki was only going to be a small cameo in the conversation between Whitbeard and Shanks. Oda didn't have an actual story for him, and when the Anime stuff came to him and asked for a movie character, Oda decided to use Shiki since he wasn't THAT important in the manga. Is it possible that Shiki will appear in the current story? I mean everything is possible but highly unlikely! I highly doubt that Oda would have used Shiki in the movie if he had a big story with him to tell. We already know Shiki's abilities, his fighting style, his crew etc. There's nothing new about him. Oda doesn't like to reveal how people look like or their powers so that he could then reavil it later in a specific time. Oda refused to show Kaido's hybrid form even against Big Mom and Oden, and you think he will bring back a character about whom we know everything? Again, I highly doubt it's going to happen.