Plot points from the animated Star Wars shows, particularly Star Wars: Rebels, have already been introduced on The Mandalorian (see: the Darksaber), so it would make a lot of sense to finally bring animated characters into the live-action universe. In particular, two characters would seem to be natural fits for The Mandalorian, because they're Mandalorians too: Sabine Wren and Bo-Katan Kryze.
Bo-Katan's current status at the time of The Mandalorian is unknown. In the Rebels era, she takes charge of the Mandalorian resistance and wields the Darksaber, and that's the last she's seen. By the time The Mandalorian rolls around, several years later in the overall timeline, the Darksaber is possessed by Moff Gideon and Bo-Katan is nowhere to be found. It seems all but certain that the show will have to include her in any explanation of how Gideon acquired the saber.
Sabine, meanwhile, would be a particularly interesting foil to Din Djarin. While he's an adopted Mandalorian who strictly adheres to their code (especially with regards to never removing his helmet), Sabine is a native-born Mandalorian who's a lot looser about observing those rules. Live-action characters have crossed over into the animated shows frequently, but the reverse isn't true, so the presence of a crossover feels long overdue.