A potentially useful feature for IDEs would be to open up the same file in a two-pane split, then “freeze” one of the panes such that it won’t change while you’re making edits in the other one. That way, you can refer back to the file as it was before you’ve started changing it.
Another useful feature would be to not assume I want to open every new file in the right pane. Choosing the pane that last had the cursor would be more useful to me.