an attempt at an upgradeable metadata function for standard NFT

Upgradeable Metadata for NFT

pragma solidity ^0.4.17;
pragma experimental ABIEncoderV2;

import "zeppelin-solidity/contracts/token/ERC721/ERC721Token.sol";
import "zeppelin-solidity/contracts/ownership/Ownable.sol";

contract NFT is ERC721Token, Ownable {

   address private metadataContractAddress;

   function NFT (address _metadataContractAddress) public {
        metadataContractAddress = _metadataContractAddress;
    }

    function updateAddress (address _metadataContractAddress) public onlyOwner {
        metadataContractAddress = _metadataContractAddress;
    }
    function implementation() public view returns (address) {
        return metadataContractAddress;
    }
    function tokenMetadata(uint _tokenId) public view returns (string _infoUrl) {
        require(ownerOf(_tokenId) != 0);
        address _impl = implementation();
        bytes memory data = msg.data;
        assembly {
            let result := delegatecall(gas, _impl, add(data, 0x20), mload(data), 0, 0)
            let size := returndatasize
            let ptr := mload(0x40)
            returndatacopy(ptr, 0, size)
            switch result
            case 0 { revert(ptr, size) }
            default { return(ptr, size) }
        }
        // return CloversMetadata(cloversMetadata).tokenMetadata(_tokenId);
    }
}