We can't pump the water higher than 83 m, because the glaciers in the ice age didn't bring higher heaps of sand than that. A cooperation of southern Germany and Switzerland doesn't make much sense either, because all these pipes would be ugly, and a reservoir on each summit would be  taking things a bit too far, I guess. No matter where you try, you will always have only very limited opportunities to build pumped hydro. We will need many more methods to store energy, combined with methods to steer demand.