From EIP-1:EIP stands for Ethereum Improvement Proposal. An EIP is a design document providing information to the Ethereum community, or describing a new feature for Ethereum or its processes or environment. The EIP should provide a concise technical specification of the feature and a rationale for the feature. The EIP author is responsible for building consensus within the community and documenting dissenting opinions.
"Ethereum Improvement Proposal" <-- this is precisely what this is. There is a (large) specification maintained in a separate repo and this is a concise proposal on how to use that specification to improve Ethereum (i.e. to reason about the motivation, to provide a reference to the "canonical" spec, and to commit to this as part of the roadmap).
This EIP is also a tool for "building consensus within the community" as a place to point to canonical-ness of a single deposit contract and release of the specs, as well as a singular place to discuss the ultimate acceptance and integration of the phased eth2 as part of the protocol.
I actually would argue this EIP is "Core" because it is designed to expand the consideration of what the Ethereum "layer 1" protocol is to include the PoS beacon chain, and is a commitment to a series of breaking changes (most prominently the swap of Ethereum's PoW consensus for that of the beacon chain).
I also expect much of the stateless ethereum work to manifest as similarly structured EIPs -- a concise motivation and reference to a larger spec -- because these specs, too, are also being designed in an independent spec repo