I think it would be mandatory to listen for the TransferSingle, TransferBatch (ERC1155) and for the Transfer (ERC721) events to automatically list new NFT’s in your web3 api. Otherwise it’s not possible to have any real interactions for NFT’s. For example someone can not build a NFT market place because most tokens aren’t even indexed. Also cross game NFT’s are not possible becuase the token of the other games are not indexed in the web3 api. The only way this is useable atm is with NFT’s that user create in your dapp or with your contracts.