App Switching on iPad with Keyboard

On OS X, "command-tab" switches rapidly between applications.

On Windows, "alt-tab" switches rapidly between applications.

However, when using an iPad with a bluetooth keyboard, there is no easy way to switch between applications using the keyboard. Sure, I could reach up and switch between applications with a four finger swipe, but it would be much faster and more convenient to do this via the keyboard. Command-tab is probably one of the most used shortcuts on any computer, by anyone

(a) Does anyone know how to achieve this?

(b) If this is impossible, could the good people at Apple pass this feedback to someone who could implement it? So easy, and such an important shortcut.