Hello @kieransimkin
It does seem that there is a lot of interest in this. However, there may not be a need to extend/ add anything to 721. I think making a proposal for a completely different standard would be better.
It will allow all those that want to maintain 721 close to industry standards to keep it as is, while new format will allow you to fully explore this format with out having to sacrifice anything to old format or make changes to other CIP 25 additions harder to implement.
Plus you will avoid having your features being shut off. Example:
Your format would allow a viewing application to immediately call API for such NFT. This may pose privacy concerns, since anyone could create such NFT, send it to someone’s wallet and would instantly know when that person opens that wallet because they can monitor that specific API call.
So, any wallet would probably just shut that feature off, or at least give an option to shut it off.
If it was a different standard then 721, then any dApp/ wallet/ website can just choose to not support such feature. While on line viewers or other dApps can choose to support it.
Also, any site that renders the NFT could set up separate limits for this new standard. So, if an NFT is created to attack the rendering site by flooding it with info during the gathering stage, data limits would protect against self DDoS while not affecting regular 721 NFTs.
Having this as a separate standard may allow you to avoid a lot of friction that you would get if you just try to append this to 721.
Very interesting proposal btw. Looking forward to seeing how all this develops.