There are many reasons I had to explore the embedded metamodel subgraph design pattern for Neo4j databases in the first series of FactMiners ecosystem design documents.
My interest is grounded in my experience in the 1990's developing a pair of complementary Distributed Smalltalk frameworks to do what we called "executable business models." The basic idea was that if we came up with a super-elegant metamodel about how to do business processes AND STUCK TO IT no matter what on the server/executing-model side of things then the Desktop Visualization framework could dynamically generate what customer/users mistook for "applications." We found INCREDIBLE leverage in design-to-implementation and stakeholder buy-in (as what we built made sense to them... it was their mental model embodied in software).
We can bring this kind of leverage to graph databases, and I hope Neo4j will be the pioneer leader in this, by coming up with a community standard for an embedded metamodel subgraph feature.