That's an avenue that's also being pursued, but it's not obviously superior to other storage plans. You've got lots of moving parts under high load, you need enough structural support to ensure that the top-heavy structure is stable.

It also doesn't contain a huge amount of energy - 1 ton of liquid NaCl contains about 700MJ of usable energy, you'd have to lift 700 tons of material 100m to contain the same in gravitational potential.