Theres tons of ways that people with even a little brains could figure out, the problem is often cost or feasability.
A big burried water tank in my yard could be heated during the day and used to warm the house via underfloor heating at night, could do the reverse with chilled water in the middle of summer plumbed to an air recirculator with a heat exchanger. Its really simple engineering but expensive to implement.
I think an awful lot of people just dont understand the sheer scale of a lot of these problems, not the fundamentals.
Oh yeah,I'm no expert. I can see salt being problematic if the system sprung leaks and contaminated the soil which wouldnt be uncommon once you have tens of thousands of houses rigged up. Im pretty sure most water based systems just use water and antifreeze.
Point is that the fundamentals are simple, when theres excess electricity and nobody is home convert it into stored thermal energy that can be used later when people are home, the devils will be in the details.