There’s nothing deregulated about forbidding futures contracts.
There are really two alternatives here. One is that solar+storage never manages to provide cheaper electricity than existing nighttime baseload generation methods. Then the big change is that time of day metering becomes cheaper during the day (when solar generates) and more expensive at night (when baseload generators justify their existence). But that isn't going to destroy the power grid, it's not a fundamental change, it just changes the pricing.
The other alternative is that solar+storage does become cheaper than baseload generation methods even at night. In that case the power grid is destroyed because most people simply stop needing it. It becomes cheaper to over-spec the solar panels on your roof and the batteries (or whatever) in your basement to handle unusual conditions, or suffer not being able to run your air conditioner one or two days out of the year, than to pay the full cost of operating the power grid just to handle those one or two days a year. But in that case there is nothing to privatize/nationalize/whatever because the residential power grid simply ceases to exist.
In my opinion, electricity needs to now become a government function. The more people install solar panels and batteries, the less profitable electricity is going to be.
It's a death spiral eventually completely dominated by the fixed costs of keeping the network connected and enough electricity production in reserve rather than the variable costs of baseline consumption.