Since the release of Dragon Ball GT–the previous sequel to Dragon Ball Z–was completely erased from continuity, though it may not stay that way as Dragon Ball Super has subtly set the stage to making GT canon once more.
As opposed to Dragon Ball and Dragon Ball Super, Dragon Ball GT wasn’t originally a manga but was strictly an anime series, a fact that has always hurt its legitimacy as a Dragon Ball continuation. The series followed Goku after he was transformed back into a child following the villainous Pilaf making a mistake while wishing upon the Dragon Balls. Despite being a little kid, Goku is later able to unlock his most powerful form yet: Super Saiyan 4–a more primitive and unique take on the Super Saiyan transformation that pulls inspiration from the animalistic roots of Saiyan heritage. While the form was powerful and uniquely awesome, it was cast aside into the hypothetical void of non-canon Dragon Ball content alongside Super Saiyan 5 and Krillin with a nose. However, one key artifact introduced in Super could change that in an instant.
In Dragon Ball Super Chapter 16 by Akira Toriyama and Toyotarou, the Supreme Kai of the Tenth Universe, Gowasu, is training his successor, Zamasu, in the ways of being a Supreme Kai both in of power and duty. One of the main functions of a Supreme Kai is to watch over all life in the universe and help it thrive while being sure to not get too involved in the natural progression of any particular species. While watching one primitive race, Zamasu doesn’t see their worth and thinks of them as lesser beings because of their barbaric lifestyle. So, Gowasu shows him a way to jump forwards in time and see the species’ progression in an instant, hoping that doing so will change Zamasu’s mind. To do that, Gowasu uses an artifact known as the Time Ring which is kept in a case alongside four other rings. However those other rings aren’t rings of time, but rings that were created after the timeline was skewed by someone who tampered with the past, creating an alternate timeline in the process.
Those rings kept in the Supreme Kai’s possession are gateways to other realities that parallel the main Dragon Ball timeline. Since fans haven’t been given a full explanation on each one of those other timelines, it is possible that one of them leads to the universe of Dragon Ball GT. If that theory were to be proven true, then entities from either timeline could use the rings to travel to the other–creating an adrenaline-pumping, action-packed crossover event for the ages while also reestablishing Dragon Ball GT within the overarching Dragon Ball canon.
So far the only alternate timeline fans have seen through the use of the rings is the one created by Trunks after he went back in time in the hopes of preventing the rise of the Androids in Dragon Ball Z. Other than that, they are a complete mystery both in of how they were formed and to where they lead. Given all the room fans have been given to speculate as well as the fact that Dragon Ball GT is a previously established universe with interesting ideas and character designs that shouldn’t be abandoned, Dragon Ball Super has potentially set the stage for GT to be made canon, and no one even noticed.
