If 77% of power can come from rooftop solar when far less than 70% of people have rooftop solar, then you'd expect prices to rapidly decrease for consumers. Unfortunately retailers are now able to sell power that get access to almost for free (solar feed-in payments have been heavily decreased it looks like). This will only further incentivise people to get their own panels, increasing the grid instability. It is actually in the networks best interests to put downward pressure on prices in this case, otherwise they'll need to front the costs of managing an unstable grid.
I imagine we are approaching a tipping point where the cost of connection to the grid is more expensive than provisioning a home with enough solar + battery capacity to go fully off grid.
Depending where you are, then it's already happened.
Rural areas - a decade ago they were quoting A$18k per pole, and you'd need one pole per ~70-100 metres depending on terrain.
Of course, in rural environments you're more likely to want / need three-phase, and other high-draw appliances -- but conversely you've likely got access to much more roof or ground space to put panels, fewer restrictions on sizing and location for storage systems.
Well 77% is domestic roof-top solar, so it doesn't take up any land.
As for the other 23%, according to Wikipedia [1], South Australia has 2 operating solar farms (338 MW installed capacity), which take up 1000 hectares, so 10 km² (which is about 0.001% of the State's land area). SA also has about 2 GW of wind power.
