It is seem to the authors of GIL are interested in generalized image data structure. However, many users require some specific function for their aim. How about, namespace "GIL:: specific" is used for contributions for specific aim? "GIL:: specific" will provide generalized (don't depend on data structure ) specific functions. Relation among other libs also important.
However, you can rely on third-party libraries to do this, for example http://www.antigrain.com/ (<=2.4 uses a quite liberal license) and http://www.cairographics.org/ . Both can render to memory buffers which in turn can be used directly in GIL. How about relation to other libs locate in GIL::binding::other_lib_name (antigrain, opencv … and so on) (Like ublas::binding::other_lib_name(atlas , lapck …), . GIL::binding::opencv is already exist. http://www.codeproject.com/vcpp/stl/stl_like_coding_with_mmx.asp