Nice diagrams. I love it when a plan comes together.

One recommendation would be to remove the section_ids (as the records are self describing) and instead add a value (in bytes) to the header with the offset to the first record of each type.

For example in your sample the offsets would be
0x01 = 4800000000
0x02 = 9F00000000
0x03 = BC00000000
0x04 = 2A01000000

Alternatively you could include a claim_type record for each type just after the header and before the array of claims which has the type, offset, count, value, size but that might be overkill.  The last option would be to not include the section size or section header (i.e. header then list of claims much like a block is a header and list of txns).  The snapshot will probably be parsed to a database (at least key value db like leveldb) for processing anyways.