You can likely build something SQL-like to form complex queries coordinating related objects, but the efficiency of such queries is not a given. You can likely manually build something like an index to speed up lookups using e.g. the map primitive. With a plan for a complex query, you're on your own.

Another likely problematic part is PK generation. You can of course use a counter, but I'm not sure how efficient will it be with burst inserts. For that, you'd have to come up with client-generated PKs that are unlikely to clash, e.g. UUIDs.