Have you used QtQuick (particularly the QtQuick.Controls package) in Qt 5.1+? Because based on what you wrote I believe it covers a lot of what you're asking for here.
Unfortunately it doesn't look like these are available yet in Python, as Python doesn't seem to have bindings for QtQuick 2.1, at least based on my googling. Hopefully that will come soon though!
(and the latest installer tagged Qt5.1.0 contains a QtQuick.pyd)
While I see the benefit of using python for brevity in areas Ecmascript doesn't cover (file access, pipes, io, etc) I'd personally just write whatever scripts I was going to use inline with qml as js, because I already can assume v8 is running underneath the platform, and js is pretty fast, so think about it as an interim solution. You can actually write whole qml apps that never compile and just run on the qmlscene binary (which is just a shim frontend to the qtquickengine internals of qt to run qml files).