I tried Nouveau NVC0 Gallium3D from Mesa 17.1-devel Git this morning. I was running the Linux 4.10 kernel and had enabled NvBoost=2 mode and re-clocked the graphics card to its 0f performance state. The NVIDIA graphics card for this open-source driver testing was the GeForce GTX 780 Ti Kepler.
Unfortunately, when launching Civilization VI with Nouveau NVC0 on Kepler, I got a black screen... Right away, it didn't get far at all.
It wasn't a hard hang, but was able to switch to a VT.
Civ6 ended up having a segmentation fault in the Nouveau driver and there are various Nouveau DRM errors and TTM buffer eviction failures reported.
Well, at least another new test case for the community developers working on the open-source Nouveau Gallium3D stack. If it were to run, it would probably be fairly slow even with the re-clocking and boosting given the results we've seen with the NVIDIA proprietary driver and RadeonSI Gallium3D driver -- check out those articles if you haven't done so already.