That may be the case but if you look at the commit history of cstore_fdw on Github, it's not that active. Also, none of the paid Citus customers were using csto

That may be the case but if you look at the commit history of cstore_fdw on Github, it's not that active. Also, none of the paid Citus customers were using cstore_fdw with Citusdb last year to my knowledge so that was not their focus even though this was the initial idea. The Citus engineer that I asked this question was not even sure if cstore_fdw can be used with the distributed version of Citus. My conclusion was that most of the Citus users use it for OLTP workloads since PG doesn't really have a distributed query planner that works smoothly with the OLAP workloads.