That's a really good idea, but every tool would need to apply the same concept or no one would be able to edit them. On another view of this, the scripts are initilized on entry of game and/or mission. Thus, if I am not mistaken, increased speed would only apply to the transition from one area of the game to another.
Currently, the speed of this does not really bother me, but the frequency of crashes and slow developement does. XML would fix this. Binary could too, but unlike XML, creating a format to use and programs to decript the binary code generated by FS2 would take much longer. XML could be intergraded into FS2 and FRED smoothly and slowly without hindering developement (provided that an XML Notpad translation program is created first).
Never-the-less, if the FS2 team and FRED team were willing to take the challange and time to reformat in binary code, I would fully support it. As long as things are done right, it could produce the same results XML produces and increase speed between transitions within the game. But again, it's a great deal more work and harder to apply.