Well, Steam is going cross platform, but not all their games are. We are hoping to port AI War to Unity 3D in the late summer, which would give us OSX support right there. But Unity 3D does not yet fully support linux, so I suspect it would be down to how well WINE supports Unity3d-based games. Not something I have explored in great depth yet, but it's something people are welcome to try out with Tidalis (demo or whatever). If Tidalis (either the OSX or Windows versions) can be made to work on Linux, then AI War should also work on Linux once we port it over to Unity.
And, heck, hopefully Unity 3D will announce full linux support sometime before too long. It seems like it would be comparably easy versus a lot of the other recent portings they have done / are doing (360, PS3, etc). But a smaller market, too, I guess. Maybe the Linux support will come when they start doing Android support, too.
