I’m surprised to see that Unity engine does not support Linux. Since you have already developed a runtime for Mac OSx, why not make a plugin for Firefox / Chrome Linux?
There are so many render engines that work for Linux; Web GL, OpenGL 3D, QT4…
What’s the point of making non Flash based games if you are going to limit platforms?
Unity SUCKS for not making multi browser / OS runtimes.
Unity 4 and up support publishing to Linux(specifically Ubuntu as of this writing).
Unity Technologies still do not provide a Unity Web Player for Linux browsers. I also haven’t heard any plans on doing so.
Workaround:
Previously Linux users tried to install Windows versions of internet browsers to run the Unity Web Player using Wine.
The Pipelight project has made a plugin for native Linux browsers. It still uses Wine, but at least you won’t deal with Windows versions of internet browsers. See the community set up wiki page - http://wiki.unity3d.com/index.php/Running_Unity_Web_Player_on_Linux_using_Pipelight