As an owner of a MSI GTX970 4G, I can confirm that with 4.12-rc1, I can boot
perfectly fine with a single monitor connected, and with Mesa 17.1.0 on the
userspace side, my user experience with KDE Plasma is thus far
indistinguishable from the NVIDIA blob. Awesome work there, kudos.

Plasma's Wayland session does freeze shortly after login, but that's not
supposed to be mature and can be caused by any amount of things.

Now, if I try to add a second monitor, I get corrupted output after modeset
seemingly, but I'm pretty sure that's bug 89664.