Well, I'll give them credit for a potentially intriguing idea. Making Diesel's character, who's been the lynchpin of the group in the past few movies, go bad could work, but if they don't give him a really good reason for this turn, the movie'll likely crash.
I'm still a bit iffy about this one, not so much because of Walker's death, but because of how the last movie was. The outlandish predicaments in that one, like jumping a car from one highrise building to another, got over-the-top to the point of cartoonish, and if they try to keep going that route it'll actually end up getting boring. If they can ground this movie more back in reality, rely less on such crazy stunts and more on the characters and how they interact, it might work.