I think the first assertion is simply untrue, and without it the rest is nonsense. You don't need to learn how to use multiple editors to do anything.
I suppose there are some languages/environments that are somewhat tied to certain editors (java and eclipse, C# and visual studio, objective-C and xcode), but that's not what is proposed here. It's a general purpose programmer's editor that anyone can use for anything. Are you really upset that it's being written? Why do you think you'll have to learn it?
I think it's also worth mentioning that Atom, like Sublime, looks straight-forward out of the box. You don't need to learn much to be productive. It doesn't have the learning curve of vim/emacs, but it's more powerful than Sublime/Notepad++/Gedit etc.
Also, I don't think anyone needs more than one general purpose text editor like vim or Sublime or Notepad++, and possibly a full-featured IDE like IntelliJ or Visual Studio. If there's a counter-argument, I'd like to read it.
I suppose there are some languages/environments that are somewhat tied to certain editors (java and eclipse, C# and visual studio, objective-C and xcode), but that's not what is proposed here. It's a general purpose programmer's editor that anyone can use for anything. Are you really upset that it's being written? Why do you think you'll have to learn it?