Some ideas, if everybody havent leave civ 5 for civ 6... (maybe some have been said i havent read all the threads )
Workers can sit(work) on an improved tile to increase its yield
Workers can turn to militia when in war ( must be activated before it gets attack or it just gets capture ) could be available with Honor policy
Improvement: training ground; unit standing (training) on it for a complete turn gets xp
Trade routes to other civilizations who has a luxury you dont already have gives 1 happiness.
A remake of Great Heroes mod, including admirals with correct attack animations and era evolution
I would split most of ressources, like unstead of gem , have diamonds, rubys, saphir, emeralds, unstad of fish, have tuna, salmon, shark, trout (only in lakes) , different timbers, oak, maple, pine ebony