Many projects will need the ability to mint randomly generated NFTs that will have an amount of possible permutations that is impossible to pre-enumerate in an IPFS files. Some NFT projects will also build the NFT from the token ID itself, and need to listen to events for creating an html file with a filename of the token ID.
This is almost trivial with a nodejs API on your own server, and the metadata works perfectly with AWS Lambda, but this introduces centralization risk into the equation.
If Alchemy ran ad hoc metadata and file nodes for NFTs, it could secure this server network with either trustees from the ENS, being a subsidiary project, or by forming it's own DAO with a governance token issue to the community to appoint these trustees.
While it wouldn't be as decentralized as the Ethereum blockchain itself, the intent is to move the integrity of dynamic NFTs to a more secure service. An L2 for metadata. I believe Alchemy with its resources and knowledge is the perfect candidate to implement this service.