Samsungs latest DeX dock allows the Galaxy S9 to be used as a trackpad, a feature that Huawei already supported in its own PC mode and Microsoft in its Continuum before that.
Android P may bring official support for this and even add the option of using the phone as a keyboard. A patch for this was committed back in December 2016, but has been disabled.
Using a phone as a trackpad is pretty okay, though the typing experience wont be great. Still, simplifying the controls to something like joystick sounds nice e.g. an extra controller for your console. Alternatively, it could be a standard way to control smart appliances over Bluetooth press any key to do the laundry.