According to Shiina, a prolific Fortnite leaker who specializes in the battle royale, Epic is apparently working on a new Fortnite update for Season 3, which may come out on August 30, and that version 21.50 should be released, since the X1 updates normally go live a week later. That would theoretically mean Fortnite v21.51 should be released on September 6.
Although it's been quite some time since the last concert, v21.51 might contain more information.
Film seems to be less likely, though. Epic usually presents Halloween-themed films in October (of course), and having a separate, un-themed showcase as close to the holiday one does not fit Epics style.
Other commenters on Twitter noted that the X1 updates usually don't contain anything too big anyway. New cosmetics are the current favorite guess, since most assume this update will be a minor one. Epic recently added a Fortnite Dragon Ball Z crossover to its ever-growing roster of crossover skins, and while it may seem like too much to expect another DBZ cosmetic so soon, we're still hoping.
This is Fortnite, so anything is possible.
If you're still working through the Dragon Ball content, check out our handy guide on how to complete all the Fortnite Dragon Ball challenges and where to find the Kamehameha locations. We've also made it simple to find the capsule corp capsules and compiled each Dragon Ball episode code in case you missed any.