Pyqt-5.1 was released today.
http://riverbankcomputing.co.uk/news/pyqt-51d

Seems to work just fine so far. Had some rendering problems earlier but that turned out to be a gpu driver problem but I upgraded my graphics stack, and now it runs smooth as silk. Qml2 runs in opengl, on linux at least, so your drivers must support that.

Outside of namespace changes the only problem I've run into so far has been that you have to use super() with multiple inheritance in pyqt5. And I can't for my life get my friggin imageprovider to work. The requestPixmap method somehow takes one parameter less than it should and then qml just spits out "TypeError: invalid result type from ImageProvider.requestPixmap()". I've tried anything I can possibly think of in my own code ... could be a bug in qt or pyqt. Other than that it seems to work just fine. Hopefully it works good on arm/wayland too on Sailfish.