I think the GDL editor has become quite outdated. Nemetcheck borrowed gdl editor used for its smartpart looks much better. I would propose an easier writing in the gdl editor with commands indicators and color highliting, such as nemetcheck allplan. Or simple interface improvements as in notepad ++, codeblocks ... etc.
Smartpart editor Nemetcheck allplan. It has line numbering, hints for commands, style color for classic comands, information of parameter of command at the base of the editor.