Except the Linux community isn't expecting you to support SteamOS alone, they want you to support Linux at large
As part of the Linux community, I'll have to disagree. This also came up the last time Steam on Linux was discussed . As was concluded there, each distro can implement their own package that installs steam and any missing dependencies necessary to get it to work. Alternatively, the user can devote a small partition to Steam OS and switch out when they're done working for the day and want to game instead. In fact, the user can install SteamOS and separately install the steam client in their main distro and have them both share the same game install folder and only boot into SteamOS when a game isn't working as well as expected in their favored distro.
That said the developer can just choose to support SteamOS and leave it at that. As a *bonus* the game should work in other Linux distros.