My last talk at PGCon tried to fill some of the gaps around what you must know to hack on Postgres, especially the Executor Phase and TupleTableSlots. I'm not the most qualified, but sometimes it takes a learner to know what learners need. Just the other day I wrote a table of contents for a book about how to contribute to Postgres. I figure it would sell at least ten copies. Maybe a serial publication online would be better. Curious if anyone would be interested in either of those?
For now Postgres is more like a hobby for me, but if someone is hiring to do open source Postgres contributions full time, I'm open to a chat. ;-)