You can use python to play with the GPIOs…but i am not sure ‘how’ you’ll be able to read values sent from other devices like the HC-SR04, to do stuff.
I did something similar with my pi1: http://www.instructables.com/id/Automated-cooling-fan-for-Pi/
But as you can see, i only used the GPIOs to turn on/off a relay.
If you have any experience with arduinos and you have a relay, an arduino pro micro (or nano, or any other arduino) you could program the arduino to use a HC-SR04 (ultrasonic sensor) to detect movement…and if a person pass by the sensor to flip the switch on the relay that will give power to the raspberry.
Then just get a slideshow plugin in osmc, and set it to start after a few seconds when it boots up like he did:
A simple sketch for the adruino to use the HC-SR04 and detect things: HC-SR04 by sandbird