Improved Xlib support is now available for Self 2.0.1, in the ftp contrib directory.
From the README:
This package provides improved Xlib support for Self release 2.0.1. The Xlib primitives are now dynamically linked (release 2.0.1 has statically linked Xlib primitives). Many primitives have been added; in particular, drawing primitives are now present. In addition, it should be simpler to add new Xlib primitives by following the examples present in xlibTemplates.self and using xlib_glue.make (see the manual for details about glue).
This package is compatible with release 2.0.1, including the ui. The interface to some of the Xlib objects may have changed slightly.