FoundationDB endlessly interests me and even though the record layer is nice, my dream would be a proper SQL layer. I've been experimenting with making Postgres run on top of FoundationDB, effectively making Postgres a stateless layer itself, and it actually works surprisingly well as a POC.
Had been pretty quiet for a number of years, but two pretty sizable capabilities have been added in the last 6 months, which looks much more alive: predicate pushdown and roll-up aggregation. https://github.com/FoundationDB/fdb-record-layer/pull/2916 https://github.com/FoundationDB/fdb-record-layer/pull/2746