Oh, that's exactly what I want, and have been researching for myself. I'm taking it even further and planning on being able to switch individual circuits between battery and grid.
If that idea is dumb somehow I'd love to know more resources about why. From my perspective it's a better solution than grid tie, but I value resiliency and reliability as well as pure cost alone. If I still lived in a city where the power literally never went out for years at a time, then having a local backup would not be really attractive.
And considering the regulations, it seems like the system I'm considering would also be able to basically satisfy the desire for "i'll make the first 5khw". Select a circuit that draws at least 5 kwh/day, run it off batteries until the battery bank voltage drops below a threshold, and then switch over to the grid.