I don't know where you got the impression from that Neo4j can't handle graphs of this size. We have users and customers running much larger graphs in production. So that _definitive fact_ is not true :)
I'm willing to believe that Neo4j could handle it (admittedly this research is 18 months old), but everything I see about the Neo4J licensing model indicates we could not link to it without also opensourcing our code, which is a no go for us.
That ~5B edges is roughly where we're currently at, however that is growing and the limit of 34B is under 10x of where we're currently at.