Minimum One Physical Button for Apps

I think smartphones should have, at a minimum, one physical button that can be accessed by apps. I want to make that physical button easily configurable. This is how I think it should work:

1. A very simple Android setting (and widget) to link the hard button to the app of your choice.
2. For each app, the ability to select one or more default actions to be invoked by the hard button. (These only occur when in step #1, you have chosen to attach the hard button to that app.)

The cell phone is like a really big Swiss Army. It bristles with utility, but that can cause a bit of lag when trying to whip out the right function at the right time. So what I am after hear is 1-click ease of invoking the right function at the right time. Some use cases:

• Starting the camera, and putting it in your chosen mode
• Starting myTracks and beginning to record
• Invoking Navigation, to the pre-defined default destination
• Mute button
• Starting the stopwatch
• Texting

Here is a bonus idea for implementing this--if the physical button is invoked with a long-press, it bypasses the security screen, for that application only.

UPDATE: 10/07/16 This last thing is what double-pressing the power button does on some Android phones.