It's not likely that one would uses ones windlass and bow thruster at the sametime. The cables are already there why not use them for double duty?
First, cables for windlass are about 4 sizes too small. Windlass cables are rated for 50 amps (and it really only draws 30-35). Thruster is 100 amps at least.
Secondly, it can't really be done because windlass control box is near the batteries so the cables are direct power to it. I'd have to move control box and have power up on it all the time. And then the breakers are rated differently.
These are very different devices.