I'm running two different GNU/Linux distributions, none is Debian-based, and they are both "pure 64-bit", so no multilib installed (which is necessary for Steam because it's 32-bit). But I wouldn't use Steam anyway. It would be nice if there was a generic Linux 64-bit release which is not bound to a specific platform/distribution. This of course depends on the libraries used to develop the game (most do work on GNU/Linux).
I realize I am a minority though. You probably won't have many requests like mine, and if that's the case, no need to bother. At any rate, your game looks really interesting.