That would work best as a watch "complication". Pulling phone out, turning on, finding app, tapping activity button takes too long; much easier/suitable to turn wrist, tap icon (adjacent to clock), tap activity. Good idea, if implemented with zero friction.
Fortunately IFTTT Do has a widget you can stick to your homescreen and even your lock screen.
Now if only it was a bit faster :( I use it to turn on the lights of a belkin wemo and it takes ~9 seconds for the light to respond, and frankly often doesn't work (in which case you get a helpful email stating it didn't work). But it's certainly much, much faster than using the Wemo app.
That's a cool idea. Pebble doesn't have a touchscreen, though. You could program one of the shortcuts (long-press one of the 3 right-side buttons) to open the list or even activate a specific activity directly. Assuming such an app ever launches!
