It is probably not helpful for Timestamp to list Snapshot's hash

Timestamp and Root are likely to be the two most-downloaded files on a repository. Currently, Timestamp lists information for Snapshot in a different way than Snapshot lists information for Targets and delegated targets files: timestamp lists the hash of snapshot in addition to the version number of snapshot. It is not clear that this is actually useful.

The costs to this are a few:

• It adds size to the timestamp role file (one hash where timestamp would otherwise not contain hashes)
• It makes the timestamp role file a little harder to read and understand.
• It makes conceptually reconciling timestamp and snapshot definitions a bit harder for implementers / new folks.
• It requires a bulkier and less intuitive programmatic representation (in formats.py and tuf_metadata_definitions.asn1).

Snapshot definition
Timestamp definition

Start by reading the linked Snapshot and Timestamp definitions in tuf-spec.md, then inspect formats.py and tuf_metadata_definitions.asn1 to understand the current representations. The work is done when the Timestamp definition and its programmatic representations no longer include Snapshot's hash, while the stated version information remains consistent.