I've got a rather long list of stuff I'll send your way later.

But the #1 most important thing I would say is the editor should be as drop-in friendly as possible.

Include a generic version of all (or the most practical) systems used in the game.

That way when someone downloads the editor, their mod is ready to go even if it's just three characters thrown on an empty map. In the D:OS 1 version, having to add stuff to the _Start goal, alignments files, and things like that are a huge roadblock for a lot of people. Especially if someone wants to use some of the commonly used gameplay aspects of D:OS like waypoints, attitude, shovels, mining, etc. Just getting those to work right now involves either rewriting the script from scratch or extracting and cleaning up the MAIN files.