There are other "costs" besides electricity costs as well though. Quality of life at home is impacted with the noise and heat produced by mining hardware. Not everyone will have the ability to segment parts of their home to where the heat and noises is minimally invasive on their home environment. That being said, as hardware becomes more efficient in it's use of power, reducing the heat dissipation and fans, this could turn into something more palatable for the returns on mining. I think it is good to see Samsung putting their effort behind it, since it could accelerate that ability.