I think the OP would like to choose some kind of low power sleep mode in ES to "shutdown" the Pi, but not completely turn it off. And then OP wants to be able to wake up the Pi simply by pressing a key on an attached keyboard, just like how you wake up a Windows computer or Mac.
I don't understand why a special hardware should be needed, but I am also confused why there seems to be no simple software option to enable such behavior? In fact such behavior should be the default to safe power with sleep, and allow easy wake-up by pressing space or any key or clicking the mouse, just like is has been on any PC or Laptop for a decade, and such is the default on pretty much all set-top boxes like Roku, and consoles like PS4 and Xbox One consoles, too. However, on those, it is a button on the remote or wireless controller that wakes up the device, not an attached keyboard. Using an attached keyboard should be simpler, since Bluetooth is not required to be kept on.
EDIT: Apparently, in order to save cost as much as possible, the Raspberry Pi board has no power management whatsoever, e.g. no sleep/suspend modes, no wake-up, nothing compared to what is found in most other modern hardware. There are a few add-on boards that provide such power management, such as sleepy-pi or witty-pi, but bottom line, there seems to be no easy way to do what the OP requested.
