Hi Matthew,

Not an answer to your questions, but a few remarks that might help anyway:

• while a single client has its limits in adding vertices and edges, people use distributed computing frameworks such as Apache Spark and the like, to increase overall ingestion rates

• sparql-gremlin was not abandoned but included in Apache TinkerPop: https://tinkerpop.apache.org/docs/current/reference/#sparql-gremlin

I could not help doing a singe Google search request myself and hit upon:
https://github.com/IBM/expressive-reasoning-graph-store
which seems pretty recent, though immature.

Best wishes,   Marc