As someone who frequently goes months without playing CDDA and then returns, I quite liked this thread! With that in mind, here are some notable (to my mind, that I came across) experimental features since 0.D:
Static NPCs and z-levels are on by default
A fully functional item favoriting system
Hunger becomes based on stomach volume instead of kCal
Add speedloaders for many guns
Add 3 new NPC AI rules: not open doors, not move into an open doorway/obstacle, not investigate noises
Use fuel from firewood source when starting fires
Add trait “Deaf”
Radio contact with followers, NPC overmap movement (first step)
Added a new bionic that nullifies negative enjoyment value from any comestible with negative joy
Gravedigging
Add almond milk, soy milk, and a method to produce almond milk
Adds new pet armors for canines with crafting recipes