This may not be outright confirmation they'll appear in the story, but it does make it much more likely that Dragon Ball Z's Saiyan and Frieza Saga are represented in the game, to some degree.

The long-awaited battle between Vegeta and Frieza will be a pivotal moment for Vegeta's character arc. There is perhaps no other character in all of Dragon Ball who ... the Namek Saga, it was ...