A significant portion of Saul’s story has already been devoted to Jimmy’s time after Heisenberg’s reign of terror, which means Aaron Paul’s Jesse Pinkman could show up on his doorstep after escaping from his prison in the Nazis’ compound.
This development naturally raises very important questions about which characters could show up, and where we may see them.
However, that’s only one aspect of the show.
In the primary Better Call Saul storyline (which takes place in 2002) we could easily see characters like Hank Schrader, Steve Gomez, or even the dynamic duo of Badger and Skinny Pete make appearances.