Hi there!
I'm Tyler, the X-Plane developer in charge of the UI for X-Plane 11.
Support for loading a situation via command is missing from the current release of X-Plane 11. The upcoming X-Plane 11.10 will replace it—you'll be able to use the Load Flight window to bind a practically unlimited number of situations to keys or joystick buttons.
Until then, though, it's not possible. :(