I know power switching is being considered for our next ROV version, as part of a broader electronics overhaul. Beyond that, I don’t believe we’re working on a self-contained power-switch that could be added to an existing ROV.
The biggest issue with an ROV power switch is being able to handle the significant current levels that the thrusters can draw. If “low power” is an acceptable “switched off” substitute then you might want to consider using a switch to control a MOSFET that can switch the power inputs for everything other than the ESCs, or possibly just the input to the 5V converter. Both those options mean the flight controller can be switched off, at which point it cannot send any control signals to the ESCs (which means they’re safely stopped), and should reduce most of the idle current draw.