The article mentions but does not explain why the other languages are not to the task of today's programming needs. For example, the article mentions Python but dismisses it without explaination. Python is very powerful, readable, productive, mature, self consistent and can easily tie into high performance C/C++ libraries using SWIG. It can be used like a glue language for lower level high performance code.
For example, with Python you can call the OS optimized OpenGL libraries almost function for function from Python. This means you don't have have special documentation for Python as you would for Java with a 3D library. There is tons of OpenGL example code out there that was written in C that can be very easily made to work with Python. Only minor changes are necessary.
PyObjC allows replacement of Objective-C for Cocoa programming and it works better than Objective-C. Python is definitely the best language I have seen for programming a Mac.
Any time you create a new language it takes years for it to become mature enough to use for serious work. This includes developing the language and the support libraries. Languages like Python have been through that and I think offer any benefits you may want in a brand new language. (Ruby may be similar, I just have never used it).
The Programming World Needs a New Language