I still don't think the copper/silver analogy fits in here. Its...

I still don't think the copper/silver analogy fits in here. Its not about finding a bigger supply of metal and saying why aren't people starting to use it instead of what is the current standard practice.
I'd liken it more to the invention of Structural steel. Previously people were using timber or stone to build houses and other buildings but it has limitations. You can't build a skyscraper or the Harbour bridge with timber studs. Then you find a way to make steel columns and beams at an affordable price so eventually you start making bigger and more complex structures. But at the same time you don't use it to frame up a typical house because it doesn't make financial sense to do so.
To use that analogy with LiS, the batteries they have developed will only be used where capacity to weight is an issue. Stationary batteries used for Grid storage don't have any weight requirements so it make sense to use a different chemistry that is cheaper to produce.