[EDIT] it's also not nearly as well-supported so you'll find a lot of supporting libraries with multi-datastore support don't support N4J yet, or do but only in some crippled or poorly-tested (not widely deployed) fashion.
[EDIT EDIT] it's also not a great fit if you have a lot of constraints on or structure to your graph. At least as of when I used it ~1 year ago it had essentially no support for expressing things like "this type of node should only permit two outbound edges". You can work around that but the solutions will be less safe and/or suck.
Constraints and hosted multi-datastore solutions aren’t really an issue for me, but the type of query you mentioned about subgraphs might be. One query I know I’ll need is one that can quickly identify nodes with lots of neighbors that have a specific property.
The data is definitely very graphy, so I really wanted a graph database as the primary. Dgraph seems pretty good (advertises itself as more reliable and faster), but it sounds like graph databases might just be kind of oversold in general, and that I might want to reconsider. One other issue is speed of development, which the graphql plugin really increases, so I’ll probably stick with Neo4j for now. Swapping dbs theoretically shouldn’t be THAT painful if I don’t care about migrating data and keep the graphql layer the same.