Gonzo's screen time was minimal in the last film due to him being used as a brick joke. He was present in almost every single deleted sequence. I'm sure they're going to give him a much more substantial role this time around. If nothing else, I doubt he's going to spend the last 20 minutes of the movie revving up a bowling ball throw.
As for Rizzo, his biggest role in the classic three films was MTM. Even then, he shared screen time with the rest of the rats. His appearance in GMC was a line in a song. He only blew up in the next three post-Henson films. The last film was going for a classic film/the last 3 films didn't happen feel, so it does make sense why they'd ignore Rizzo and Pepe. Still, I don't see why everyone sweats that when we had Uncle Deadly in a major film role.