Earlier quoted context omitted.
Customers could keep their grid connection for backup purposes, but it should be rarely needed. Therefore if a customer is acting 99% self-sufficient, the grid operator is going to lose out. And this could happen within years when battery tech becomes cost effective. This change in legislation has just served to shorten that timeline.
Just keeping the grid connection is a major cost.
I've never lived anywhere where I used zero kWh for the month, so I'm not sure... but I have to imagine the cost would be pretty slow... save for getting such a system setup (transfer switches are common enough with backup generator situations so I can't imagine that portion would be very expensive)