Yup - we will definitely support SteamOS in particular.
SkookumScript builds on pretty much anything that has a C++ compiler. (Its runtime is written in C++.)
We just haven't been building for anything other than Windows and iOS for the closed beta to minimize the amount of building and testing that we need to do for each revision.
First we will support the SkookumScript runtime across platforms and then we plan to have a OS/X and Linux version of the IDE as well (and a Windows IDE revamp).