@Vlad - right, native components! I keep forgeting about that.
Is there any native component like "attached window", not "menu"? Something like this:
and then you have more freedom in designing the window's content - you can use elements that look draggable. Finder does this in sidebar:
Safari does that in sidebar too:
Another example of sortable list:
Quick sketch of how it could look:
It kinda looks similar to existing interface, though 🙂