You may have already seen my answer in LinkedIn message.
Hyperledger Indy has a very specific purpose (identity) and therefore the chain of trust is important. They write the steward and trust anchor roles into the ledger in order to enforce the trust level.
Hyperledger Fabric is more a generic platform. If you wish to use it in Indy-like application on Hyperledger Fabric, you can develop your chaincode and apply endorsing policy on a specific organization who has the “steward” role. The distribution of identity and credential should be off-chain, as what Indy is doing today.
If you notice, Hyperledger Aries now takes a ledger agnostic approach and we may see in future that the identity application running on Hyperledger Fabric provided that a proper resolver is created.
Hope this helps, and thanks for your question!