On the other hand, drive storage is super cheap compared to the past so may be more efficient to store as the same format it came in as, and only use RDB or other indexing for lookups
Discussion
Wouldn't NoSQL be more efficient, once the data set gets much larger?
For storing the nostr events to return yes. But not necessarily for searching unless sticking to the limited filters from NIP-01
Partitioning by field values/ranges, and other stuff like POW score, hashtags referenced, key phrases referenced are better suited for dedicated indexers imho