I wrote about this very issue as a limitation in my whitepaper.
"Although we feel that Hyperledger Fabric is the best solution for enterprise blockchain use cases, we did find
some limitations in the solution. Currently, data is encrypted before it is stored in the chain code. If the data is
shared with all the nodes, then all nodes will have a copy of the encrypted data but they will not have the key
required to encrypt the data. The potential issue with this approach is that data on the ledger is immutable and
can be potentially held there for years. At some point, years down the line, our quantum computing power will
evolve and todays encryption technique will be compromised and may expose all of the data across the nodes.
But with proper governance in place, an organization can adopt a proper migration strategy to mitigate this
risk."
But I'm not sure what we can do to protect against this, are there any serious projects that are addressing this need?