While I can see the need for DIDs somewhat, I feel like content-addressing documents fits the decentralization paradigm much better when it comes to a lot of types of data.
While it doesn't have all the properties of DIDs, it has the most important ones, and comes with some other nice ones (automatic deduplication).
I may be wrong, but are you thinking of DIDs as an ID for an object, like CIDs in IPFS. If so, then you are confusing what DIDs are for. They're created as a method of using some distributed network as a backend for a entity (could be a Human, could be another machine) to store their identifiers on. These entity's can take actions, like signing a doc and uploading it to a blockchain. The DID in this instance is the record of verifying who this entity is, and if they should be trusted to do that action.
Content addressable IDs, or CIDs in IPFS are used to identity a document or object.
So the distinction here is objects (some record of data) vs entities (something that can take actions).
For a lot of use-cases cases I don't see a need for a distinction between the two (if you don't have a requirement for mutability, revokation, etc.). Especially in recent developments in the decentralized space, it seems to me that having most data (regardless of object or entity) be immutable and content-addressable, makes reasoning about systems a lot easier, since you don't have to worry about the data you are pointing to changing from under you. Of course, different use-cases have different needs.
> The DID in this instance is the record of verifying who this entity is, and if they should be trusted to do that action.
I don't see why you wouldn't be able to use a CID for that. As long as the content the CID points to contains the record of the entity, and a cryptographic signature, you could do the exact same thing.
Except in the DID instance, you can represent a DID using a CID. This is how IPFS creates their implementation called IPID[0]. DID is a schema/protocol for DID and DDO, and its associated content. Its one step higher then a CID.
Contend addressed documents wouldn't fit directly into what DID is trying to accomplish. A DID is supposed to be a unique id to identify an identity, such as a Person, a company or even your pets. A DID maps to a DID Document that may change overtime, e.g.: the public keys listed in it. If we were using content-addressing for the identifiers, they would be changing over time, which will be hard to use in a variety of systems.
This doesn't mean that we cannot use content-addressing. For instance, in IPFS world, the DID could actually be using IPNS to point to a CID. This allows to have a persistent DID pointing to CIDs at different times. There's actually a DID method called IPID (based on IPFS), that uses a strategy similar to this.
Unfortunately, much of the information we interact with every day is ever-changing and published by someone specific, which is not a feature provided by content-addressable storage.
Depends on what content-addressable storage you mean specifically. IPFS (disclaimer: I work on IPFS) handles this by using IPNS together with your PeerID. As long as you have the ID of who the "someone specific" is, you can listen for their published changes. The changesets themselves are immutable, but IPNS provides a mutable naming layer on top of that.
That, then, is not content-addressable storage, and is instead an entirely different part of the system bundled in under the same name. I'm not sure what benefit such a thing actually provides, anyway.
Sadly not that much from the top of my head. I mostly became familiar with it through IPFS[0][1], but the Wikipedia article lists other projects that might have interesting resources[2].
Disclaimer: I'm working on a project[3] to create a content-addressable version of OWL2 (Web Ontology Language), so I'm certainly a bit biased.
While it doesn't have all the properties of DIDs, it has the most important ones, and comes with some other nice ones (automatic deduplication).