Hi @cryptodate - late to the party here, but I just saw your post! Are you still looking for more support for ERC721 orders? I’d love to revive this thread and listen to your concerns.
I’ve developed an API that allows anyone using any programming language to create orders on the 0x protocol (721, and soon 1155 if there is demand) for NFTs. This API is similar to the 0x Swap API, but specifically designed for NFT order creators like market makers or NFT marketplaces. It can be accessed through GraphQL or REST API with a single request, and returns call data for both the maker and taker that can be easily settled on the blockchain. This makes it easy for users to discover, evaluate, and implement the 0x Order protocol.
You can see my other thread about it here and I’d be happy to share an access key so you can test it out!