Just came across this thread and found it interesting, so I’ll try to offer a few suggestions. I think the honest answer is:
For tx inclusion proofs, the practical first step is likely not Flyclient, but exposing CKB’s existing get_transaction_proof / verify_transaction_proof path through Cellora. That lets clients verify that a transaction is committed under a particular block header, rather than merely trusting Cellora’s indexed result. This easily moves Cellora from a purely trusted indexer toward an inclusion-verifiable indexer.
For full historical / chain-tip trust minimisation, my narrower point is that I’m not sure there is a canonical Rust/TS wallet-side verifier package that app developers can just plug into today. So for Cellora v1, I’d probably keep MMR/Flyclient-style support as a later integration layer, not a hard requirement.