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
