It would be nice if these ebuilds had a USE flag description that explained that Wayland and X11 support are (apparently) mutually exclusive.
Example output from mupdf:
gl error 65544: Wayland: Failed to connect to display
cannot initialize glfw
We in GNOME are likely to flip on global USE=wayland flag in gnome profiles within a month or two when 3.24 goes stable. That doesn't mean that people will actually use a Wayland session, but that they have a choice for that. Thus it making X11 not work at all is quite unexpected, if truly the case, and it should really support both at once or only one if both USE="wayland X" are present and only one is chosen.
So I'm not fond of USE=wayland being used at all in a way that makes X not work without any warning really; maybe a IUSE=X and a REQUIRED_USE between them if it's not a common package? But that's inconvenient as well.
I was wondering what Fedora does as that now defaults to a GNOME on Wayland environment. It seems they just build it for X. Then again, their package doesn't have any reverse dependencies. They don't use it in their mupdf package.
*** Bug 620056 has been marked as a duplicate of this bug. ***
How about we rename the flag to IUSE=wayland-only?