I play Sid Meier’s Civilization VI (6) via Steam. The leader scenes often are black screen. The support from Aspyr told me, that Mesa 17.1 or greater cold fix this. Only tumbleweed has that out of the box, but I can’t even run steam or tumbleweed (perhaps someone can fix this). Mesa on Leap 42.3 (where steam works) only has 17.0.x. Is there a safe and sensible way to have Mesa 17.1 on Leap 42.3? Thanks for any suggestions 
Games like Civilization often only support Nvidia proprietary graphics. But it is not recommended (and probably diffucult) to try to use proprietary nvidia drivers on tumbleweed, so the obvious choice for (casual) gaming is Leap.
“There is no pre-built version of the NVIDIA driver for Tumbleweed. Tumbleweed is updated too frequently to provide a driver in time for a snapshot. It is not recommended to use NVIDIA drivers for openSUSE Leap on Tumbleweed.” from: https://en.opensuse.org/SDB:NVIDIA_drivers#Tumbleweed
Can a user put a newer Mesa version on the system by oneself? Is this recommended? Or should/can I make an “update request” for Leap? Is there even a chance of getting implemented?
This is complete ********, you can use the proprietary nVidia drivers on Tumbleweed just fine - I do.
All you have to do is add one of the various nVidia repositories on OBS that install dkms+download the nVidia drivers for you, f.ex. the Bumblebee projects “latest” repo:
http://download.opensuse.org/repositories/home:/Bumblebee-Project:/nVidia:/latest-beta/openSUSE_Tumbleweed/
Note, these will only work for newer cards (GF5xx forward -> or so)
Also, if you install/use the nvidia driver, the Mesa version should not matter at all IMHO.
Nvidia replaces the Mesa libraries with its own proprietary versions that only work with nvidia cards and the nvidia driver.