I would like to suggest adding support for public keys. These may be PayNyms from BIP47 or NPubs from Nostr. Both of these public key types could be useful. Paynyms allow for more private use of bitcoin compared to the address reuse inherent in Counterparty and Nostr npubs allow the connection of assets to identities
e.g.
pubkeys": [{
“type”: “paynym”,
“data”: “PM8TBezmLDmeWTWyMLLfZq8APFU34VTqU7aBjvj9srzNDFJqE7s3bk2jfR2ytVsWWSyf5jWUEAnwFghdEpTd7AsDUkg1NAaRPcCMXt4pzgvoR3odnGDk”
},{
“type”: “nostr”,
“data”: “npub1d4ed5x49d7p24xn63flj4985dc4gpfngdhtqcxpth0ywhm6czxcscfpcq8”,
}