We have crossed the 5 year line, the rules are stable so where to now? My thought would be to revisit an undelivered goal from the beginning modularity. The recent UA that provided alternate class features showed that modular rule packs can be used to alter the game system without undue damage to the game. Th DMG with it's scattered modules of varied value was not enough for many and there are several attempts in it that could use polishing. Books with this sort of idea could be set by theme and carry both GM an player materials which is something the designers stated early on is there preference so each book would have a wider audience. Examples could be a book that goes into damage and healing. Detailing various systems for taking and healing damage. Alternate class features for healing. Extensions to medicine skill as well as healers kits and herbalist kits. Diseases and poisons could be made more prominent in game. Then of course some spells and feats. many have clamoured for Naval matters to be looked at and Ghosts of Saltmarsh didn't scratch the itch. Some want some strongly the planar themed rules/abilities. There are so many things in 5e that have only been lightly touched or left alone and I believe we are at the point in 5e that the designers can be more explorative with mechanics and the material. Thoughts?