Or, say, your Samsung washing machine detects on your home network your Bosh fridge and try to use any vulnerability to brick it (and the fridge tries to brick the washing machine too). Appliance war...

If people know this, it would be a incentive for consumer to buy all from the same brand. If all manufactures knows this, they would need to pay more attention to security (or at least resilience).

Not sure what/who wins in the end

They'll be hacking each other and fighting with knives and silverware when your back is turned.

Imagine having to discipline your appliances after they blame each other for starting it.

the black mirror we deserve

I'd be more worried if my dishwasher found me an annoying jerk.