Ghost Rider could be what saves this show's future. Now that they've be re-legitimized, and now that Hydra is gone and Hive is defeated, they need some new reason for SHIELD to exist. Simply hunting / mistreating Inhumans, as they've become the replacement for Mutants in this timeline, is gonna get old fast unless they can quickly get a team to be a shoe-in for the X-Men.
And as much as Hive has ruined Quake, they need to do something to redeem the character - or finish her off. Once again... after season 3, the show lacks a sense of purpose. Ghost Rider gives it what it needs.
For starters, it shows that Coulson was wrong: Hive didn't inspire the Devil, it was the other way around. And with aliens and spies no longer around to bother SHIELD, it would seem that they now have to quarrel with demons.