It doesn't sound at all unreasonable, but I would just point out that there are keyboard shortcuts for that. To show and hide the file browser, it's Command-Option-Control-D. If you don't like that shortcut, you can customize it.
Thanks for reminding me of that. It must be significant that I had forgotten – the mouse gesture has become more natural, with all the other things that work that way. But as I said, it’s only worth having if it’s easy for someone to implement. (Don’t look at me, I’ve just about given up programming.)