Exactly what the title says. As of today's patch (11/2/2023) Shoulder Launcher now functions as a Hand Slot power, interrupting- and being interrupted by- other Hand Slot powers such as Hand cannon and Plasma Beam, while being usable alongside Shoulder Slot powers such as Eye Beam and Mini Gun. Previously, Shoulder Launcher was a Shoulder Slot power, and its tooltips- all of them- still list it as a Shoulder Slot power.
Pictured: the (admittedly cool) aesthetic of Shoulder Launcher and Mini Gun being used at the same time (Shoulder Launcher counting as a Hand Slot power when it's supposed to be Shoulder Slot.) Not pictured: Shoulder Launcher overriding- or being overridden by- a Hand Slot power, but you can spare me the effort of using OBS and feeding it through a video-to-gif converter by seeing it for yourself on a blank character in the powerhouse.