They're very close to the 10th film, if they want to set up an end point but also get as much money as they can from the brand, they could look at that one as the end point.
Maybe they can even milk more money by dividing the final story in two parts, then they could advertise The Fast and the Furious X.
By the way, what does everyone think about those proposed spin-offs? They seemed to be talking a bit about them before, strange that they haven't mentioned them since Furious 7's release considering how successful it was. To be honest, something only focusing on a character like Hobbs would feel a bit too much like just another generic star vehicle action movie. Only spin-off i think would bring anything new would be Tokyo Drift 2, as it would pretty much be its oun series of films more like the first three, where the focus remains on street racing.