Ok all I going to share some ideas. ok I think the most important upgrade we can make on the C model it’s to pull up the WiFi link and the application. Ok this is what I propose to Costas and all of us her.
On board(ROV) 1Raspberry Pi 4, the 2 motors drivers, 1 battery , the new camera, the batt balance outside of the sphere to recharge without open the sphere. Between the ROV and the surface the Ethernet cable in a floating house and on the shore this Ethernet cable plug in another raspi and on that raspberry on Xbox joystick and one 10” HD screen in a small suitcase. No WiFI no App the good old cable and Hardware. Ok guy’s let me now if you agree. I hope my english is not to bad and you understand what I looking for.

Ok I made this schema to explain what I expect for next upgrade
I really like this idea. I think using a second pi as a monitor might be a great tool. It has all the ports you need for the ROV tether, a usb hand controller, as we’ll as 3 extra USB ports. Not to mention, this would prevent any WiFi connection problems someone could foreseeabley have while using their android device.
Im curious - are you envisioning setting the pi with the monitor as a router? And do you (or anyone else) have any ideas for what goes inside the hand controller? Since I like to keep this all open source, my mind goes to an Arduino board+PlayStation joysticks.
And thanks for the visualization, I really appreciate the work you put in, and it definitely clarifies your idea.
-Costas