Since Game Editor script is compiled to intermediate code,and not to machine native code, this request is probably not possible, but I'll throw it out there anyway:
I'd like the ability to include Libraries that have already been created outside of GE. That would be a powerful and exciting feature. It would give GE the ability to be a full featured development environment.
I am really asking this feature for the 'C' programmers that are using GE. Personally, I am a "click together" sort of user, but maybe eventually, I'll know enough to use Libraries effectively too.