I have done some research into drones, but currently lacking batteries - which has halted my drone flying project.
I have worked with high power switching mosfets, which ESC's essentially are - DC in, 3 phase output to the rotor engine.
There are written loads on the matter of ground currents, and it is a hard concept to master completely. Practice makes perfect, or at least running good enough.
When the frequencies are low (kHz), and the currents high/pulsing - I often get most design ideas/precautions from thinking the wires as the transmission line in my car, a transformer as a gearbox (here the ESC's) and the wheels/rotors spins. A shaft can go through something, if shielded well enough, and out the other without problems.
HUGE & HEAVY - Something I don't want to be close to unshielded.
Electrons are lazy, and take the easiest way on their electrical way - but they're also taking the hard way + the extremly hard way + sometimes impossibly hard way. Oh, they also love being paired - wire wise, so twisting +/- minimizes the EMI emissions quite effectively. Good for EMC compliance, less good for design looks, manufacturing and breaking during a crash - insulation tears
I recommend running the high pulsing power train/bus-bar very much separately from the flight controller/RF(high-power away from flight controller)/Videocamera(also away from high power RF)/sensitive stuff - wrapped in Cu foil, a custom built flexible Faraday cage.
If you need a ground (and you'll need one as you're up flying around), do a star-configuration at best possible physical implementation, so the currents to any on board device are it's own on that set of wire. The controller PCB is a good starting point, as it most likely has an effective internal ground plane and hopefully already prepared for this.
A lowpassfilter works great as a noise barrier - the currents to the various onboard devices are low, so low losses in transferring useful energy, and great blocking of unwanted energy. The wires are thin, potentially saving weight. The filter might not, it comes down to how it is implemented (physical blocking - switchmode transfer - extra battery - )
Oh,
Get a working system, then start cutting away wires to optimize flight time.
You'll know when you hit the limit, either in a good way or in an expensive one.. crash, please don't burn