Current filesystems are software-defined on top of block-based storage, I don't see a reason why we can't still have software-defined filesystem layers built on

Current filesystems are software-defined on top of block-based storage, I don't see a reason why we can't still have software-defined filesystem layers built on top of key-value-based storage. The key-value storage just lets you potentially keep a more meaningful lookup id versus block storage so could offload a little bit of work from the filesystem layer, while keeping the exact same filesystem API in place.