Interesting. The Da Vinci Jr ( and maybe others ) have a similar setup, with a single flat wire connector carrying current for sensors, heater and fan. I agree with cgimark there are several issues.

1- too much current in the wires for the hotend heater. I see you are already using 3 pins to supply each power and ground to the heater. I think that is too few. Heres why: For example, is you plan on a 40 watt heater, that will use 40/12 = 3.33 amps. Allowing for safety, assume 6 amps. Flat ribbon cable is usually 28awg, and can carry 1.0 amps , yielding a 3.3% (0.4 volts) voltage drop for a 3 foot distance. For 6 amps, use 6 wires for the + AND 6 wires for the ground. ( see https://www.powerstream.com/Wire_Size.htm ). Better solution is as cgimark suggests, separate connector to deliver the hotend current.

2- orientation of the big connector will results in poor flexibility for the direction of movement. ( based on you pictures ). Either rotate the pcb 90* or the main connector.

3- solution would be only for a single axis of movement hotend carriage ( like a Cartesian ) due to the 28 pin cable flexibility.

You design looks nice, a few minor changes and I think you have a solution. Thanks for sharing.