What about just using Vim, Emacs, nedit, gedit, or whatever your favorite editor is on UNIX/Linux? Why do we need a special editor just for Unity when there are already plenty of good alternatives?
Unity3d comes with Mono Develop (http://monodevelop.com/). That's their default editor. However, you can easily switch to Visual Studio or whatever you want. You can use gvim if you want. If you pair up Unity with cygwin and git you come pretty close to what Linux gives you. I'd still prefer it if they ported the editor to Linux, since it would mean I don't have to boot Windows.
Unity3d is not a text editor. It's similar to Blender... it's a UI for manipulating 3d objects and setting various components of those 3d objects. When you need to edit the scripting of an object, it launches the external text editor.