Would I be able to play this with my friends who have Steam copies, or am I out of luck on that front? It's just direct IP connection multiplayer so you'd think it'd be okay, but maybe Steam has a different MP design or something. Just asking.
The Steam version uses Steam software for communication (which can't be used out of Steam).
The gog version uses another software for communication that is not compatible with Steam.
Therefore, I'm afraid it's not possible to play gog-steam.
That isn't cool at all. Could you see if there's a chance at least in some future update? I have played some games that allow it (like Hammerwatch for example). I prefer purchasing on GOG for a lot of reasons, but I still want to play with friends who have the steam version. A couple of friends recommended me the game (and they have the Steam version) and now that it has a linux version I'm thinking of purchasing it.
Another question, I supose it will be possible to play multiplayer with different versions (I mean Windows and Linux versions). Or am I wrong?