I completely agree with Marc. You can try adding those features and rest assured, you'll have one of the best xml editors by your name.
I specially feel the "Find" (Ctrl+F) feature is one of the most important ones in any editor. I was trying to use this editor and was happy until I found out that I cannot search for a particular word in the file. Hope you'll come up with this
I also like the syntax check feature. Helps a lot.