Tangentially: I use a variation on this, but I do it as a custom keyboard layout system-wide. From a US keyboard, I rotate () → [] → {} in that order (associated character → new position), based originally on frequency analysis of X captures of my keystrokes from a decade or two ago. Nowadays I also swap ` over to F9 and rebind the ` key to Compose (leaving ~ alone), since I use it a great deal for extended punctuation.