This is a simple app that uses the Muzei 3.0 API to save the currently displayed Muzei wallpaper to your downloads directory.

Step 0: Obviously your current wallpaper should be Muzei 3.0+.
Step 1: Tap the icon in the app drawer or use the quick settings tile.
Step 2: Select where to save the image.
Step 3: Profit? Nope because this app is FREE!

Hint: Power users (like me) will associate this app with a gesture perhaps via Nova Launcher.

Free and open source. Download the code here: https://github.com/banasiak/MuzeiSaver