Ethereum: has or will Ethereum back up its software with a hard asset in the future? only if the unthinkable happens!
Each full node hosts a copy of the chaindata, which contains the current state of the Ethereum Virtual Machine. Chaindata can be copied to any storage device large enough to host it. A digital backup of the chaindata would be the most effective form of backing up Ethereum.
Individuals can back up their own digital assets physically by storing their private keys somewhere safe. Cryptosteel offers a good solution for this. A cryptosteel holding a private key, which controls digital Ethereum assets, would be as good of a hard asset as any.