Enabling the editor and then visiting an article in the administrator site, PHP will fatal-quit because it requires(!) a php-file within the editor switcher directory named like the installed editors.
A quick peek at the code shows it iterating over all installed editor-plugins and require_once()-ing a plg-local file.
Thus, the downloadable package seems 1.) incomplete, 2.) untested.
I also question the concept being used here in general. It means the editor-switcher would require a PHP file for each editor you install. And it will not be able to provide these for custom installed editors or custom editors.
I want you for me to help for a GPL license.
Of course, although I am testing, it cannot test in the environment which I do not know.
Then, please tell me the editor which you have installed, and environment.
In addition, it is only the selected editor that is requiring.