For #1, in terms of scalability, yeah, you could self-host keto, but they also don't support core functionality like zookies or rewrites (e.g.

permission x = y + z

) and we aren't API compatible, so if you eventually didn't want to run it yourself or needed to scale, you'd be rewriting your app code. The easiest thing should be to let us run things for you, rather than trying to run something yourself -- we even expose our internal metrics so that our users can fully integrate their systems into their own monitoring infra. Our pricing is pay-as-you-go, so small instances should be in the free-tier most likely. For #2, if you can find that paper, I'd love to read it and share it with the team (and everyone in this discord, haha). Neo4j is a general purpose graph database, which when used for authz would be called a GBAC system. Zanzibar systems explicitly limit the types of queries you can make and the structure of the data so that it can be fully denormalized so that results are cached time for most queries.