Where things will go from there is hard to say, although given John Cena’s popularity, I suspect his time in the Fast & Furious world won’t be a one-and-done thing, and that he could return for Fast 10.
Evidently though, he hates Dom so much that he’s willing to team up with Charlize Theron’s Cipher, the main antagonist from The Fate of the Furious.
Aside from Jakob Toretto not having been in Dom and Mia’s lives for a long time and being a skilled thief, assassin and high-performance driver, we’re still largely in the dark on what his deal is.