I think they are trying to attract web developers here, which makes sense since web developers or hybrid web/desktop devs probably outnumber desktop focused devs right now.

Out of these millions of web developers, regardless of which stack they use Javascript is the one thing they have in common whether they love or hate it.

The lines between web and desktop are blurred to a point anyway, and there are plenty of people out there with experience developing rich applications in JS.

I'm guessing the play here isn't so much to get people to write gnome3 apps from the ground up but to focus on making it possible to give rich web apps first class gnome3 support with the minimum of extra code.

Of course other bindings will continue to exist for those who prefer to use them.