If you look at PV there were similar "ah ha, costs have stopped falling!" moments in the past (mid 2000s, for example), but they didn't last long and were followed by even more dramatic cost declines. It's important not to be selective here, like climate change deniers are looking at global temperature data.
Why don't batteries scale to grid level? I don't see how this assertion could be justified. Do you mean a specific KIND of battery?
Renewables + storage certainly could provide 100% of the needs for the grid, in a properly designed system. At this point it's just a matter of quibbling over cost. Since the world could be spending upwards of a quadrillion current dollars on energy in the next century there's a hell of a lot of financial headroom to scale things up.
There's no proven nuclear technology that scales to power the world either. Do you accept that as an argument that nuclear should be disregarded?
It's entirely reasonable to assume that some storage technologies will survive being rolled out to the scale needed to allow renewables to reach 100% penetration. After all, there are thousands of different battery chemistries, and many other non-battery storage technologies, including ones using 19th century levels of science (pumped thermal storage, for example). Your negativity requires that all fail. I think you doth whine too much.
