How many films can Dom Toretto and family possibly support? Especially in the aftermath of Paul Walker's death? Universal seems to think two more (after the one thats' coming out). Just two more movies? Why not get us to Fast Furious X? C'mon Universal.
The studio wants to end the series and they want to do it right, by bringing back Justin Lin. While Lin didn't start the Fast and Furious films he very much defined them, directing all the installments from Tokyo Drift through Fast and Furious Six. James Wan took over for the forthcoming Furious Seven, but he has stepped away from the franchise to make The Conjuring 2 at Warner Bros. Universal won't want to wait for him (and my understanding is that there's no point in waiting cause he ain't coming back), but they could wait for Lin to direct the first two episodes of True Detective season two before shooting the final films back-to-back.
And ending to the Fast and Furious movies? What could possibly end this saga except for the deaths of all involved? This isn't a story, it's an epic that sprawls across continents and decades, an ongoing ode to the joys of stunts and family. These films could go on forvever and ever, amen.