I think it will never be the case that you can run a household solar/battery plant for less than a utility can do it on massive scale and just run a wire to your house (remember to factor in depreciation on all your household kit, batteries and inverters don't last forever).
I think this applies more on the battery side than the solar side. There are certain options for storage that are totally impractical for home use. For example, vanadium redox batteries [1] are so bulky that you probably don't want to put them in expensive residential real estate, but they're pretty cheap and effective.
But a mix of residential solar and utility-managed batteries could be viable; it's not clear to me that the economies of scale for large solar installations are very strong.
I think this is true too, but it depends on how efficiently the utility company runs their business, and how much profit margin they are allowed to extract.
Utility companies aren't competing directly with each other for the lowest price, so in practice there could be a lot of places where, while less efficient, it's cheaper for home owners to have their own means of power production.
