1) having some indicator of what has changed in a file would be killer. Hippoedit and notepad++ show vertical lines in the gutter. The thicker line indicates lines in the editor which have changed since the last save. The thinner ones indicate lines that have changed in the current editing session and have already been saved. IDE’s all have this. There’s no reason why editors can’t. It’d be killer in combination with a good integration with VCS (I like mercurial).
In EmEditor, if you display line numbers, modified lines are displayed as thick bold-font line numbers. I hope this helps.