When using weston with the xwayland.so [core] module, one can (try to, currently) starts x application from within a wayland session. For this weston opens a socket and starts a specific xorg server on demand. This 'specific' xorg server requires the -wayland option to be available in xorg-server, and this is currently not available with x11-base/xorg-server-9999 This ticket is about having proper support for xwayland in x11-base/xorg-server-9999
Sorry. This isn't the kind of thing we're going to maintain as a patch to a git ebuild.
To clarify: XWayland support isn't upstream yet. The reporter thought it was, and that adding support to -9999 would be the addition of a configure flag.
I confirm, thanks for your time!