Wallets like Metamask probably don’t use the ENS Metadata Service directly. But they do use the same normalization code (the very same code that will be updated in the near future). That same code gets embedded into ethers.js and other major libraries, which in turn gets used in major clients/wallets like Metamask. If the name is invalid per the normalization code, then Metamask will not allow you to use it:
The NFT image for invalid names will be that red image you may have seen before:
So your avatar won’t “work” for the name either, at least not on any major client/website/dapp. For example, LooksRare doesn’t delist the name like OpenSea does, so you can still see the image:
So yeah, it’s a voluntary service, of course. It doesn’t affect anything at the actual contract level. But for many people, I think they would find usability diminished, because it:
Will be delisted from OpenSea and possibly other places
1a. This also means that the NFT for your name will disappear from most wallets like Metamask / Coinbase Wallet, because many wallets simply pull NFT metadata directly from OpenSea’s API
Will show the red invalid avatar on all clients/dapps/websites that use the metadata service
Will not actually work/resolve in all wallets, such as Metamask
But of course, you can create your own website/wallet/marketplace that doesn’t abide by the same normalization rules, or doesn’t use the official ENS metadata service, if you wish.
In addition, it’s worth noting that the metadata service gets all its data from onchain sources, is open source, and anyone can run their own and produce exactly the same results as the TNL / ENS Labs one.