The new DLC named Encounters, adds in a new medium fighter craft, five new quest lines with new characters to meet, six new primary and secondary weapons and more devices like an EMP Generator and Decoy Holograms. On top of that, there's also new G&B factory stations, new skins and finally even more achievements to hunt down and secure.
With the game being unofficially released on Steam (downloads, but no SteamOS icon), I was curious to know with the DLC release today if the Linux version would see get access. So I spoke with the developer on Twitter about the DLC + Linux support and they said:
Should go live unofficially on Steam later today. To release officially and also on GOG we first have to migrate the whole project to UE4.17
To make it absolutely clear, I also asked them directly about GOG + Linux support and they said:
Hopefully those of you wanting it on GOG will be rather pleased about this news. It's great that more people will be able to enjoy it, since it is damn fun!
See also: My thoughts on EVERSPACE.