Holger, have you tried it.
I would definitely use a GDL editor of some sort if it gave me all the windows currently in GDL (2d and 3d views important obviously) and if it just had two simple functions;
2. Subroutine minimising – would make navigating so much easier and would show you the structure at a glance.
1. line numbering.
i don’t think i need anything else.