Whether or not it is a hash of some form seems like an implementation detail.
This should probably just be called schema_revision and optional_revision_precondition.
For v1, the term "revision" isn't used for ZedTokens/Zookies anymore because they have more specific names (e.g. written_at), so there shouldn't be any confusion.

@jzelinskie Revision was a bit odd considering the read is for a subset of types, but I guess you can just read it as "latest"

That's an interesting idiosyncrasy for v1alpha1, but it won't be true if we promote these fields to v1.