Did they ever implement a SQL layer? They seemed like one of the only NoSQL products with the architecture to make it plausible to do so.
Edit: found it https://www.voltdb.com/blog/2015/04/foundationdbs-lesson-fas...
Not sure what to think of it, I'm not a DB expert by any means but the post sounds plausible enough and the SQL layer is discontinued AFAIK. I guess with each new abstraction layer you leave some perf on the table.