Games (and often multimedia creation apps) have been rolling their own UI for a long time.
So games have always been the fastest, most optimized performers on any platform.
This isn't about games though - this is about regular ol' apps, many of which are incredibly slow and could really use the 8x performance improvement that these folks have been able to achieve.
As a mobile dev myself, I don't think mobile platforms are moving away from Obj-C or Java. Sure, we have a lot of custom-built widgets to overcome shortcomings in what Google/Apple provides, but ultimately they're subject to the same performance limitations that plague the stock widgets. Nobody out there is digging into low-level OpenGL optimizations to write a custom navigation bar, for example.
Most devs use some kind of wrapper library like Cocos2d to take the pain out of raw OpenGL, of course, and they can usually get by with much simpler library of widgets than the OS itself has to provide.
If you can in _any way_ achieve a method of using the existing android ui components and making them faster, this is a massive win.