This line in the log looks kinda suspicious to me:

[    2.278551] nouveau 0000:01:00.0: enabling device (0000 -> 0003)

I am not seeing it on my end ; could this mean that the Geforce card is a
secondary display device, and that the integrated Intel graphics is the main
one?

In this case maybe you need this patch, which is not in -rc4:
https://lists.freedesktop.org/archives/nouveau/2016-April/024523.html

Also I am surprised by the report that the screen goes blank after this -
failure to initialize GR should not interfere with the ability to display a
framebuffer (only acceleration will be disabled).

Let's make another experiment: can you move /lib/firmware/nvidia/gm204
somewhere else, reboot (you will see a complain about missing firmware files in
the boot log), and tell us whether the display is active after that?

Thanks!