So what we have here is a tradeoff. IFA (native graph db) avoids the O(log n) cost. Also, it scales well in the sense that query time doesn’t degrade with increasing total graph size, only with the subgraph queried. So we weigh that against the storage complexities introduced by IFA (translation layers and pointer rewrites) as you point out.
For apps that are traversal-dominant with more reads than writes, IFA wins those tradeoffs. And what we’re building is a knowledge graph curated with the assistance of your WoT. By its nature, it’s going to get bigger and more traversal-heavy as it gets more sophisticated. And the tasks that will really push its abilities are going to be read-heavy. (Imagine searching a knowledge graph to discover surprising but useful topological similarities between subgraph A and subgraph B. Also known as “making an analogy”.)
At least, that’s my current thought process. It’s worth keeping in mind that for write-heavy scenarios with short traversals, the tradeoffs may favor non-native graph databases. And there are non-native graph databases that are built on LMDB, like TuGraph and HelixDB.