Except an insane cost of power and storage
Slip-connections, multiple small autonomous generators, construction, geographical requirements not too steep, not too flat, giant area consumption.
A pipeline, a lower bassin, and upper bassin, and a pump/generator, and water. At approximately 1/7th. the cost per MWh.
Anyhow a danish guy, Henrik Stiesdal, formly the CTO of Siemens Windpower, now retired has a danish blog called "Engineer the Future". He has a specific interest in storage, and reviewed the railcar concept when it was floated last year:https://ing.dk/blogs/henrik-stiesdal
Calculation of cost, and comparison to powerwall and pumped storage:https://docs.google.com/spreadsheets/d/17GSgnGc2hry4NOoY8dGzedkvNeQF8T-BZAn3MWaTFfY/edit#gid=1628421449
I don't ever see the mechanical gravitational systems competing with simple pumped water.