Unfortunately the open-source nouveau driver is not there yet, and their proprietary shit doesn’t even do RandR 1.2, which means no sane way for multiple-display setup with single-display fullscreen gaming, or rotation if you need that.
Thanks for listening.
On openSUSE at least, you can use the proprietary driver after installation by adding
nouveau.modeset=1 to the kernel command line (no other hackery was necessary for me). Unfortunately, the installation breaks the OpenGL driver of nouveau.