(This is with reference to src/glx/glxcmds.c; other implementations in the tree might have similar issues, I haven't checked)

In principle you might want to query GLX_VENDOR_NAMES_EXT if you're trying to do something clever with glvnd; other strings are imaginable for other possible extensions. But at the moment the call to __glXQueryServerString is unreachable, because of the 'default: return NULL;' in the switch statement. Part of the reason for this is that the `priv->serverXXX` strings are saved in the GLX display state and are manually freed at shutdown. If we returned arbitrary strings too, we'd need to track them in a hash table; and once you're doing that, why not do that for _all_ server strings.

This probably also requires making __glXQueryServerString robust against getting errors instead of replies.