Agree with all three points, and the second is especially important. A GM needs to be able to override or activate scripts in an intuitive way, and hopefully it isn't gobs of work to manually implement the lines in the editor. Some way to automagically produce the code that lets the GM set flags, change variables, etc.
Also, letting four players control characters with a 5th GMing would be nice, instead of bumping out a player slot for the GM. I can understand if there's technical limitations, though I recall them saying they could run eightish players without too many problems, maybe a tad unstable. It's hard to imagine how four players would work fine, and then five would suddenly break the engine, though of course there will always be a certain threshold to break the engine.