Autohotkey is wonderful (and I can relate to the issue of getting it accepted as a legitimate tool). I also think that the beauty of the AS/400 UX is beyond just keyboard shortcuts. It probably has more to do with consistency, context awareness and that the most important functions are reliably available everywhere. But I never worked with it myself, I only have looked over the shoulders of some green screen users, so maybe there is more to it.

Another thing is that the WIMP (Windows, Icons, Menus, Pointer) paradigm was, at least in part, born because of the insight that the block oriented approach of the green screen terminals wouldn't scale beyond a certain point. I'm more interested in the ideas that made IBM 5250 like UX successful than in a modern interpretation of it. Using keyboard shortcuts is certainly one of these ideas and so is tiling windows instead of stacking them.