ItemIDs are used to reference content in ArcGIS Online. They are guaranteed unique in the SaaS AGOL namespace, and are immutable once created, but the issue is that if a content item is deleted, then re-created, it will have a new ItemID, and all dependent items (e.g., Web Maps, Applications) will have to be manually updated. If, in contrast, it were possible to have some layer of indirection between the hard-coded ItemID and the applications that use it, then the following becomes a possibility:
1) Bob creates a feature service, ItemID 12345, but assigns it a mutable alias "AuthoritativeData123", much like esriURL.com or any other URL shortener.
2) Then, Alice makes a Web Map using the alias (ideally the system defaults to showing one if it exists, or using physical ItemIds if not).
3) Bob deletes ItemId12345 by mistake, but realizes it and can re-create the content as a new Item. However, it's ItemID is now 67890. BUT, he uses the same ItemID alias "AuthoritativeData123", so Alice's Web Map still works, and furthermore Bob does not need to track down all of the likely numerous dependencies and get their owners to update their ItemID references.
This is a bit like the concept of a C record in DNS. The physical A record of the host referenced by a CNAME can change, but this is invisible to users who only know the C alias, which is usually more human-readable. This allows administrators to change out hardware, VMs, move workloads, etc, without coordinating with numerous users who have a hardcoded reference to a particular machine.
I'm proposing that ItemIDs be treated in a similar manner - just like in DNS, if you don't want to create C records, referencing a host by the A record still works just fine, but the C records give you an extra layer of abstraction if you need it to change something at the host level. In this scenario, users might choose to create ItemID aliases for important content, and then the AGOL system would need to look and see if an ItemID alias exists, and if so, use it in place of the hardcoded ItemID.
