The news has been broken on the Let's Push Things Forward blog by Gnome developer Travis Reitter. Currently there is no official confirmation and nothing on the Gnome website.
After considering the waste that supporting many languages was creating, the team decided to do something positive:
"We spent a long time discussing the different options that are available to us, and there were a variety of opinions. However, at the end of the day, we had to recognize that no language is perfect and there will always be disagreement. The important thing was that we had to make a decision."
"It's critical that everyone understands this decision as a plan to elevate the language, bindings, tools, and documentation to a level of quality we have not yet achieved. It is not a decision to abandon any other language bindings. We will continue to distribute other bindings and documentation as we do now and compatibility for the other languages will continue to be developed as they are today by the developers involved with those modules.
It is also important to realize that this choice relates to user facing programs, i.e. end user applications. For system libraries the language of choice is still C.
The final comment is:
"This is the start of a process and there's obviously a lot of work ahead of us. However, prioritizing a single language will enable us to turn GNOME into a compelling platform for application developers in a much more effective and efficient manner."