SteamEngine would've been rather cool too... unless there is something already called the Steam Engine... or if it didn't confuse the connotation too much with other software types of "engines"
A few theories are Valve has been working on their Source 2 engine and will release it as a competitor to Unity naming it SteamEngine. Supporting win/mac/linux/steamOS etc.
Also SteamMachine might be more unique and thus easier to search for.
