Chris,
There's two things that would be really cool.
1) GUI as globals, then you could access them like characters. i.e.
// to position a gui just under another gui
SetGUIPosition(SECONDGUI, GUI[STATUSBAR].button[ 0 ].x, GUI[STATUSBAR].button[ 0 ].y + GUI[STATUSBAR].button[ 0 ].Height);
// i hope this makes sense
2) The ablity to assign interactions from script.
character[EGO].interaction[ANYCLICK] = somefunc();
I don't thing the second would be possible, but the first would be most helpful.
1) I suppose it might be possible to provide read-only access to GUI properties via variables; however, changing things would still require you to call a function since there are other things that AGS needs to update when GUI properties change.
2) Interesting idea, I'll think about that one. Though you can of course just put some code in the existing interaction handler to call the other one.