Publisher Bandai Namco Entertainment has promised that Dragon Ball Z: Kakarot will the most in-depth telling of Goku's story to date, and everything revealed so far seems to indicate this to be the case. It hits all the check marks that many expect to see in a DBZ game, such as running from the initial Saiyan saga through the final Kid Buu saga, and adds more to that pile along the way. Not only will the game include this canon material, but non-canon material like Goku and Piccolo trying to get their Drivers' licenses and original material like the ex-Ginyu Force member Bonyu have been confirmed.
Almost certainly, there will still be some stuff cut from the game, but if there's one piece of filler content that needs to be in Dragon Ball Z: Kakarot, it's the Garlic Jr. Saga. For those who are unaware, it takes place between the Frieza Saga and Trunks Saga, and it is composed entirely by Katsuyuki Sumisawa as filler material not present in the original manga by Akira Toriyama.
It follows the events of the Dead Zone movie, which could easily be summed up as a flashback, and only runs for 10 episodes, meaning it could easily be a nice little addition to the game. Garlic Jr., after being defeated by the 4-year old Gohan in the aforementioned movie, returns to Earth to seek revenge while Goku and Vegeta are still gone. He unleashes the Black Water mist on Earth, so it's up to Gohan and the other Z-fighters to stop him, with Gohan eventually destroying the Makyo star and once again trapping Garlic Jr. in the Dead Zone.
There are a few reasons this should appear in the game. First, while it focuses more so on Gohan than Goku, Gohan is a major part of Goku's life and is already getting ample attention in Dragon Ball Z: Kakarot anyway. It'd be a nice short segue from Goku's fight with Frieza to the beginning of the Androids attack, which would also give fans times to check out some of the mini-games and sidequests of the Action RPG instead of just throwing them straight into another fight.
Plus, it's a good precursor to Gohan's fight with Cell, something to re-emphasize Gohan's innate power. This would also stand in contrast to Adult Gohan, who was recently confirmed as playable character alongside Vegito, as he tries to dig deep once again to take on Buu.
On top of that, the Garlic Jr. Saga hasn't really receive a lot of attention in other games, so it would make sense for an in-depth telling of Dragon Ball Z to include it. There was a largely forgettable handheld game focused on this saga, the Legacy of Goku 2 includes Black Water Mist-affected animals but skips the saga completely, there's a spin-off handheld card game that it's 'playable' in, and the Budokai Tenkaichi subfranchise uses some of this material. But that's a incredibly small percent in context of the plethora of Dragon Ball Z games on the market.
Overall, it's hard to say whether the Garlic Jr. Saga will actually be included or not, but it does seem much more likely than in other games in the franchise. On the one hand, it would help Dragon Ball Z: Kakarot stand out even more, but on the other hand, some sacrifices are likely to be made. It remains to be seen whether Garlic Jr is represented in the game, but given that Dragon Ball Z: Kakarot's release date is inching closer, it does seem less and less likely along the way.
Dragon Ball Z: Kakarot launches on January 17, 2020 for PC, PS4, and Xbox One.