The DLC and SDK are available now. The DLC includes the mod loader function.
Despite the the first information about LUA as scripting language for EMERGENCY 5, the SDK contains the full C++ interface for EMERGENCY 5. The complete interface for EM5, the editor and the engine. I hope you can imagine what this means for the modding support of the game: You can modify the complete game. You're missing some kind of function in the editor? Just build your own component, e. g. new light editing options.