Chapter 1 had Roger’s introduction in the first page.
Chapter 50 had Mihawk’s reveal.
Chapter 100 had Dragon’s introduction in the first page.
Chapter 500 had Rayleigh’s introduction in the last page, he barely managed to get it in.
We can assume we will get a similar thing in Chapter 1000, a new character with some sort of connection to Roger like Rocks (in a flashback). That’s probably why Oda has been offscreening many things. My guess is that Chapter 1000 will have Scopper Gaban’s introduction in the current story.
Maybe we have already seen Scopper Gaban on the cover page of Chapter 631. Here we see Crocus and Laboon for the first time after the timeskip. Crocus is drinking with an unknown person wearing a Samurai or Japanese clothes which it seems related to Wano Kingdom.