...given how Xlib and the entirety of Xorg/X11 will hopeful begin to be replace in the next year or so.
Can you elaborate? Who is doing what that try to replace X. I was actually looking and buying the XLIB Programming Manual and XLIB Reference Manual (Adrian Nye) but if there is something definitive in the pipeline I may not bother.
Eh, depending on your use, Wayland will be up and coming. Many major distributions (i.e. Ubuntu) will be attempting to default to it. I'm sure X will be there for a *long* time still to come so it wouldn't be a waste. I just personally wouldn't support X currently if I were to *start* development.
I wouldn't use anything that is display server specific anyways. MacOS, Windows, *nix, *BSD, and so on will all end up using different servers, it's quite obvious you need some abstraction between them. Then again, this is like asking people to use OpenGL instead of DirectX...