Actually, the revised BlueESC will now have a single cable for both power and signal. We can do this now since we have eliminated the I2C functionality, and the PWM signal line can be in the same cable jacket with the power wires.
The new revision of the BlueESC is still under development, and will likely not be available for at least another month. Interfacing with the BlueESC will be exactly the same as with the BasicESC, with the single exception that the BlueESC is mounted directly on a thruster instead of in a watertight enclosure. You can still definitely place the BasicESCs on board your ROV, and would recommend going this route versus placing them topside.
You may have already read it, but here is an aticle I wrote recently for MATE teams that you and the team may find useful.