Thanks, I’m glad you’re enjoying the series! I actually read your article last week and thought it was an excellent compilation of ERC721 resources.
With regard to the OpenZeppelin implementation: I took a quick look at it and you’re right, they do Metadata a little differently. I’m not affiliated with the OpenZeppelin people at all (although I support what they do), so can’t speak to how their implementation will work in the future, but the difference is more of a design choice rather than one method being superior to another.
Without having a deep dive into their code, it seems they also don’t allow for an initial supply to be defined. I think fundamentally their contract was designed to be less scalable in favour of each token being “more unique” — there’s no assumption that Metadata will follow any pattern, and I think it also allows for tokens to be minted by mechanisms triggered by anybody (whereas mine assumes the token creator is the only one who can mint them).