Big things are happening with the Dragon Ball franchise right now, as the franchise transitions from the ending of Dragon Ball Super into whatever series comes next. The bridge between these two destinations will be the Dragon Ball Super: Broly movie, which will pick up after DBS's ending and inject some bold new mythos into the series canon.
In addition to re-introducing the canonized version of Broly, one of the secondary goals of Dragon Ball Super: Broly will be , to set up the next Dragon Ball series, and given what we know about Broly's storyline, it seems clear that the next Dragon Ball anime could easily be poised to kick-off with an epic and novel new storyline: the "Lost Saiyans Arc."
Broly: The Legendary (Lost) Saiyan
One of the seemingly big aspects of Broly's backstory in Dragon Ball Super: Broly is series creator Akira Toriyama going back to one of the central premises of the entire Dragon Ball saga: the battalions of Saiyan babies which were launched out into the universe, with the mission to conquer the planets they landed on, in the name of the Saiyan empire.
This narrative framework is what brought Goku to earth in the first place: he was a Saiyan baby meant to conquer the planet, but thanks to a head injury when crash landing on Earth, Goku become the planet's greatest protector, instead. Some imagery in the first Dragon ball Super: Broly trailer suggests that the there will be some carry-over of Broly's non-canon origin, in which he and Goku were in close proximity as babies, before being blasted out into the universe, on two very different paths of fate. How Broly turned out compared to Goku could form the foundation for the thematic arc of the movie - and where that arc ends up.
We know that Goku and Vegeta will have brutal battles with Broly in the film - both respectively, and quite possibly in a tag-team situation. When all is said and done, and Broly is presumably defeated, the victory could turn out to be a very hollow one, since Goku and/or Vegeta would have technically taken out one of their own - a Saiyan whose life was marred by tragedy, twisting him into a Berserker monster. After seeing that dark fate for someone isolated like Broly, and realizing their own good fortune on earth, it would make sense for Goku and/or Vegeta to get new inspiration to find more members of their scattered race.
For Goku, the appeal would clearly be having the top tier of fighter(s) in the universe to meet and battle (as the Broly trailer already hints at); for Vegeta, it would be the next step in the emotional breakthrough he had during the Tournament of Power, to be a leader to his people, and lead them back to their rightful inheritance of Saiyan pride and power. It's admittedly a major oversight that's developed over the course of the various Dragon Ball canon series: Goku and Vegeta have always known there must be other Saiyans out there, but have shown way more concern with training and fighting battles with other aliens, demons, or Androids, rather than serving as the transformative Saiyan leaders they could be.
So how would this new storyline play out? In the same way that Dragon Ball always does, obviously.
The "Lost Saiyans Arc"
As stated, after Dragon Ball Super: Broly, there's a big opportunity for Goku and Vegeta to be inspired to seek out other Saiyans that may be scattered across the universe.
It would be good storyline approach to have Earth's Saiyan protectors spend the first part of a "Lost Saiyans Arc" actually searching Universe 7 (or other universes) for Saiyan warriors, and stumbling across two or three of them who will become main players in the larger story arc, and possibly the franchise's future. These new Saiyans could be new characters, non-canon characters that are converted to canon - or both! Each new Saiyan would get the usual multi-episode arcs, with a few or all of them eventually uniting with Goku and/or Vegeta.
After two or three of these new Saiyans were onboard, things could kick into high gear with the usual Dragon Ball villain reveal. In this case, the reveal would that Goku and Vegeta aren't the only ones to have this idea: another powerful Saiyan has been gathering his (or her) people together, in order to re-establish the Saiyan race as universal conquerors. And of course, while Goku and Vegeta have just been getting started on that quest, this Saiyan villain has already amassed a much bigger Saiyan squad of warmongering fighters.
That scenario would put Vegeta into an excitingly awkward position. On the one hand, Vegeta has changed so dramatically since Dragon Ball Z, becoming a bonafide hero; however, faced with a resurgence of his race and new commitment to their original cultural beliefs, would "Good Guy Vegeta" still adhere to his heroic personality, or revert back to powerful prince and conqueror he once was? Even with the introduction of a batch of new Saiyan characters, the "Lost Saiyans Arc" could still boil down to an emotional and brutal conflict between Goku and Vegeta - which is something fans haven't gotten to see (properly) in a long time. It could also feed back into the mythos about righteous Saiyans and the Super Saiyan God - another aspect of the franchise that could use some bolstering.
That's my breakdown about how Dragon Ball could benfit from launching a "Lost Saiyans Arc" after the events of Dragon Ball Super: Broly. Does it sound interesting to you? Let us know your thoughts in the comments, or discuss with me @KofiOutlaw!
Dragon Ball Super: Broly will hit Japanese theaters in December, and is expected to arrive in the U.S. around mid-January 2019. Dragon Ball Superis currently airing its English dub on Adult Swim during the Toonami programming block Saturday evenings at 9:30 p.m. It is also available to stream on Funimation and Amazon Video. The Japanese language release of the series is complete, and available to stream on Funimation, VRV, and Crunchyroll.