I guess it was inevitable, but after much feedback on the RatRig Discord, I've decided to update this PCB design to support hotend and thermistor wiring.
The PCB is now 80mm x 41mm instead of 80mm x 30mm. The extra height adds space for four (4) JST-VH connectors, which have 3.96mm pin spacing instead of typical 2.54mm. They can also support up to 10A when using 16AWG wires.
The hotend and thermistor each have 2 connectors per PCB, rather than wiring through an RJ45 cable (too thin). One connector goes to the heater cartridge, the other would go directly to the 3D printer control board, or to the corresponding JST-VH connector on the other PCB. The connectors are essentially acting as a passthru for a quick-swap hotend assembly.
There are 3mm traces between pins 1 and pins 2. I chose 3mm to somewhat match the through-hole pad size of 2.7mm. The traces themselves can support up to 3.9A with a 5deg C temperature rise, or 7.2A with a 20deg C temperature rise. For that reason, I went a bit overboard and added identical 3mm traces on the front AND back of the PCB, so theoretically they should support double the current (7.8A to 14.4A). That idea may be flawed, so I'm not sure if it'll end up in the final v.2 board.
The 50W E3D V6 has a maximum current draw of 3.9A@12V, 2.8A@24V.
The 80W E3D SuperVolcano has a maximum current draw of 8A@12V, 3.9A@24V.
With all that being said, this setup should technically support even the craziest/power hungry hotends, but I wouldn't recommend it without proper testing and careful monitoring.
I'll sleep on this design for a bit before submitting it to the fab.
Note for owners of v.1: I'll be happy to send a free pair of v.2 PCBs to those who've already ordered v.1 PCBs. You'll only need to pay for shipping (and maybe import taxes/VAT... sigh).