In the JSON output format (Special:EntityData, wbgetentities and dump all agree here), snaks used as part of a reference don’t have a hash, and neither does the mainsnak of a statement. Snaks in the qualifiers, on the other hand, have a hash.
Do we want to add the hash to the reference snaks? Do we want to add it to the main snak? And do we want to take the opportunity to call it an “id” in those cases (and eventually rename it in the qualifiers as well)?