Earlier quoted context omitted.
It's not a new approach, though. SWT (for the JVM) and wxWidgets (C++, with bindings for more than a dozen languages) have been following it for years.
Actually SWT was one of the most pleasant experiences I've had coding GUI stuff. I always found it such a shame that it's only possible to use within the Java ecosystem. I really wanted an interface to the SWT binary libraries from other languages, I looked into it but it seemed intractable to port. If this library takes a similar approach it's probably doing something right.
I did a project last year where I wanted to use SWT, but I wanted to write the program in Python, and use CPython rather than Jython so I could have access to C extension modules like lxml. So I hacked up a solution using the Avian lightweight JVM and the pyjnius JNI-based Python/JVM bridge from the Kivy project. I should release that sometime.