Services! macOS comes with Automator for this. -- Wrap a automator workflow around that shell script and you get: https://www.dropbox.com/s/njjyfzdptrzno6h/Strip%20Formatting...

If you open it up in Automator, it'll let you see the steps, and prompt you to install it [which really just moves the file into ~/Services]. This makes it show up in every app's Services menu.

Once installed, you can head to System Preferences > Keyboard > Shortcuts > Services, to set a keyboard shortcut for it.

BetterTouchTool will do it.