Well, you could still use the multi-hash thing for the identifiers without distributing them on IPFS, though it would make it much more convenient for people t

Well, you could still use the multi-hash thing for the identifiers without distributing them on IPFS, though it would make it much more convenient for people to pirate them, because then people wouldn’t have to look up “what is the multihash for the thing with this doi?” before requesting it on ipfs.