In my experience, an always visible folder pane is just taking up precious screen real estate 90% of the time. My idea is to have the folder pane collapse to the left, appear when the mouse is positions on the left border for more than half a sec. You can also probably have an options bar at the bottom of the folder pane where a user would be able to set various attributes like “show after X seconds mouse is on left border”,“disable auto hide”, etc. This would really help when I have large subtrees of folders, and I’d have to resize the folder pane all the way to the right everytime I wanted to select a folder on the lower levels of the tree, and push it back to the left when I wanted to get back to the code.

Wouldn’t it be really annoying to have the side bar pop up when you happen to put the cursor close to the window border? You can already toggle it with a keyboard shortcut (Super+K, Super+B). I use that all the time.