There's always the possibility that, instead of using the time travel trope to go back and undo damage thereby making a better future, the most common approach, they take it in another direction. That being, people from the future keep meddling in the past, and our heroes have to constantly regroup to fight an ever-changing landscape, one that changes every time they do something, and every time somebody from the future sends somebody back. Certainly, the end of this season showed a big honkin' shift as what looks like terminator-type battle-bots have now appeared! They've got to change that future, and quickly.
It would take a really smart group of writers to take the show in that direction. I'm not sure they have it in 'em, but we'll see.