AuraTech R&D have just built the OpenROV 2.5. It’s an interesting take on the ROV model, traditionally everything on an ROV is captured and operated topside with all power, video and coms being intertwined into the umbilical. This makes the umbilical both heavy and expensive to replace following wear.
The umbilical or should we say tether on the OpenROV is simply a twisted pair copper wire used as a communication medium via Ethernet using powerline adapters. All control systems are executed onboard the vehicle and controlled via a thin client topside, the ROV basically acts as a webserver which in turn controls a PLC to operate thrusters and the camera system.
Mechanically OpenROV needs a lot of work, however from a high level control system perspective I think the client / server model could be adopted by some of the more established ROV manufacturers.