Wouldn't using tokenURI here be better than tokenUri as then the bytes4 signature of the function address in Solidity is equal to e.g. that of EIP-721?

I considered it, but I don't think 721 compatibility matters much because the ownerOf signature is different and owner lookups require custom code, so this token won't natively work with existing ERC-721 tooling.

Perhaps there are specific tools that don't need to do owner lookups but do need to URI lookups that would benefit from consistency across methods?

Personally I would like to see a compelling reason to break the superior (IMO) naming convention of capitalizing only the first letter of acronyms (it avoids situations like XMLHTTPRPC with XmlHttpRpc).

IMO naming convention arguments should be out of scope of this EIP. But a separate EIP could make normative statements on function capitalization conventions.

I was mainly arguing for consistency with EIP-721 but it's not a hard objection from my side.

as much as I appreciate the sentiment, it seems out-of-scope to me to specify the nature of the storage, as it is outside the Ethereum network

the requirement for immutability is also questionable to me - I could see a use for a URI that can deliberately be changed or change itself over time

If we don't constrain the storage, then the tokens functionally become mutable. By asserting immutability throughout, we enable applications/users to build caching systems that they cannot built if we only encourage the behavior.

Immutable data doesn't exist. From what I understand, only content-integrity assuring identifiers exist that can indicate mutation. Replication can be used to fallback on non-mutated backups. IMO, e.g. asking to "content-address" resources in tokenURI would fit better.

"Censor"able is for sure the wrong term as it can mean all sorts of non technical stuff.

Anyways, I agree with @wschwab. For interoperability e.g. between wallets, whether data is mutable or not is out of scope.

I'm not following your claim here that immutable data doesn't exist. If you ask IPFS for something by content hash, you will get either that exact thing, or you will get nothing (if it can't be found on the network). There is no situation where you would get a different result from someone else or at a different point in time.

Regarding censorable content: I tend to agree that censorable content is fuzzy here, and I wish we could nail down something a bit more concrete. What I want to avoid is people linking to content that a provider can remove at a future point in time. The goal with these badges is that they are permanent, they aren't something that comes and goes over time. If you link out to a traditional https resource, the host of that resource/owner of the domain can remove it. Similarly, the domain may be seized and changed or taken away. Something like IPFS on the other hand allows anyone to ensure the content survives, you don't have to rely on a single operator.

"immutable data"/content-addressable criteria:

I agree with you that some networks of computers can create the illusion that some data is immutable. But on the basis of a principle, the data isn't immutable. E.g. on IPFS/Ethereum/Bitcoin when you run a full node, there's nothing stopping you from going into the chain data directory and switching a few bits. You can always mutate the data. It's likely though that the system maintaining the data will notice and e.g. notably fail or repair itself. That's what I meant by "Replication can be used to fallback on non-mutated backups (in a distributed system)."

How I'd describe it is that by requesting data using content-addressing, a user can guarantee to themselves that they'll either receive the exact data corresponding to the content-address, or nothing at all (e.g. when content-address and data don't align).

I think "content-addressing" is a better term than e.g. "immutable". I guess another usable term could be "tamper-proof" or "tamper-resistant."

data availability guarantees/non-censorable:

I'd strongly opt for e.g. "highly-available data" rather than "non-censorable." From my perspective, censorship is about withholding information in the interest of a few. Data availability, on the other hand, is a term from the blockchain research world that describes the concept of retaining and serving data within e.g. a p2p network. E.g. all EVM storage has high data availability, and anything stored in the Bitcoin blockchain too.

For IPFS, actually, it doesn't have data availability built-in. To pin an IPFS content hash, one has to personally deploy a dedicated node that continues to make the content hash available within the distributed hash table. IMO, if you wanted the ultimate data availability for Soulbound Badges, it'd probably be best to store the contents of tokenUri on-chain as e.g. a struct. I'm not kidding. It's because if you outsource delivering extremely high-quality data availability to other networks not aligned with Ethereum (e.g. IPFS), it may be that one day they just go down/stop working while Ethereum still works.

Now talking about storing the badge's metadata on-chain, I think it's obligatory I bring up #735

Lets move this conversation over to the discussions-to link as I'm hoping this will get merged as a draft soon and I don't want this conversation to get lost.

Is this requirement necessary? I believe you can bind EIP5114 to any address?

The EIP references EIP-721, so it requires it (not all editors agree on this policy).

Hmm, in abstract it says that EIP5114 requires it to be bound to another NFT, and gives example of EIP721. In section "Backwards Compatibility" Its stated that EIP721 HAS to be used as a soul. I think the EIP should be more specific if EIP721 as a soul is mandatory, or is some other token or EIP also acceptable.

Any EIP that matches the interface ownerOf(uint256 id) I think is the actual requirement. EIP-721 is an example of that, as is EIP-5114.

Please use one space after each period.

Fixed.

I'm not sure why this EIP needs to exist. Are there many use cases for nontransferable tokens? Why should implementers prefer this EIP over, say, EIP-4973?

Seems like this EIP needs a Motivation section ;)

I see what you did there. I may consider adding a motivation after this has merged as a draft, but as it isn't required I would like to move forward without it for now.