This patch would definitely be useful for Citus. We indeed currently
copy all of that code into our own explain hook. And it seems we
actually have some bug. Because the es->memory branches were not
copied (probably because this code didn't exist when we copied it).
https://github.com/citusdata/citus/blob/d59c93bc504ad32621d66583de6b65f936b0ed13/src/backend/distributed/planner/multi_explain.c#L1248-L1289