I agree that older commercialized battery types aren't so interesting, but my point was about all the battery types that haven't had enough R&D yet to be commercially mass-produced.

Power grids don't care much about density - they can build batteries where land is cheap, and for fire control they need to artificially space out higher-density batteries anyway. There are heaps of known chemistries that might be cheaper per unit stored (molten salt batteries, flow batteries, and solid state batteries based on cheaper metals), but many only make sense for energy grid applications because they're too big/heavy for anything portable.

I'm saying it's nuts that lithium ion is being used for cases where energy density isn't important. It's a bit like using bottled water on a farm because you don't want to pay to get the nearby river water tested. It's great that sodium ion could bring new economics to grid energy storage, but weird that the only reason it got developed in the first place was for a completely different industry.