Left 4 Dead was a bit of a zeitgeist back in its heyday. Not only was everybody playing it, but everybody was also modding it, and so a legend in its own right was born. Though it was a great game on its own, it would be hard to argue that it was mods that made it as popular as it was on PC. Earthfall might be going down a similar path, hopefully.
Earthfall is a multiplayer cooperative first-person shooter with a near-future setting, where players have to fend off an alien invasion by using various items, 3D-printed firearms, assorted gadgets and similar technological doodahs. Before Earthfall was released, Game Watcher interviewed one of the developers and asked what their plans with modding were, but the response was essentially a non-committal. Tides do seem to be turning, however.
Holospark are pretty eager when it comes to responding to community requests made via Steam, and so when a user asked what was up with modding, one of the developers came out and said that it is something they "could consider in the future," which seems like a more optimistic answer than what was previously offered.
According to the interview with Game Watcher, the main issue lies in not having enough manpower to handle the additional workload, but given the type of game that Earthfall is, not supporting mods at all seems like a real shame.
In the end, it'll come down to what and how the developers want to work on Earthfall, but their latest responses to Steam Community requests may well be an affirmation of direction. Or, at least, one can certainly hope so.