My bug in $(URI) depends on it.
This wouldn't magically happen unless someone works on bringing the xcb backend to the supported level.
There's a summer of code proposal for merging the xlib and xcb backends but not a bugzilla entry that I could find - should this bug become that request or file a new one?
It's in progress, with the goal of xcb superseding xlib and so cairo-xlib only being used on old systems that will not install libxcb. For continued support of cairo-xlib, there is a proxy layer [cairo-xlib-xcb] until applications/toolkits move onto using xcb directly.
Clone the tree, ./configure --enable-xcb, test and send patches.
Good news, thanks Chris.