ERC721PaymentSplitter Extension Contract Proposal

🧐 Motivation

We are trying to find an official way to discretely/transparently distribute rewards among token holders. I am certain we can accomplish this by combining the ERC721, ERC721Enumerable, PaymentSplitter contracts. This would allow creators to share ETH or ERC-20 tokens proportionally among holders.

📝 Details
I have extended ERC721Enumerable and used most of the functions of PaymentSplitter but removed payees[] and made _totalShares a function that returns the ERC721Enumerable's totalSupply (or override to maxSupply if we want to save shares for future token holders).

This allows me to add two public methods to the ERC721, release(tokenId) and release(account) to distribute payment using ownerOf(tokenId) and tokenOfOwnerByIndex(account) internally.

I also added _pendingPayment(account) and _pendingPayment(tokenId) and use it to check on before token transfer for release to owner (or leaving it for future claim by changing _releaseOnTranser to false which can be set in the constructor)

I am adding this to start the dialog while I work on cleaning my code and tests before submitting my PR. I have a working prototype of this concept here 0x68ddddc10323f8b8e3fe3514dcdb70381af12e85

Start by reviewing the existing ERC721Enumerable and PaymentSplitter contracts, then compare the proposed release and pending-payment behavior with the linked Rinkeby prototype. The work is done when the design is agreed, the code and tests are cleaned up, and a pull request is ready.