Worked on this problem 10 years ago, power distribution companies were sleepy enterprise environments with workforces who were just not equipped to respond to internet technologies, let alone threats. Even the lightweight requirements of NERC/CIP were treated as alien. The best security was in the smart meter infrastructure, which was designed around redundancy and combating fraud, but certainly not national security.

I don't think this is something we fix, it's something we evolve and move on from. My impression was the only real future relative to a grid security crisis is in storage and renewables, with more localized generation. The alternative is basically nationalization.