Professions
What generally makes any RPG different from other games is its depth of professions you can pursue. From gathering to crafting, a robust and deep profession system can go a long way to keeping players around.
I added my thoughts in this green text where relevant.
Paths for productive player profession progression - Say that five times fast!
Crafting and gathering, the building blocks of any RPG alongside loot and combat. I've admittedly gone back and forth on whether you have professions be account wide or character specific, so for now I've settled on a blend of both. The direction any individual game would take with Professions likely comes down to the design of other systems in the game (i.e. whether you have a focus on a single character, if your attention is more spread onto alts, or a blend of both). Regardless, the goals for Professions should be to provide the right incentives for players to engage with each other in a friendly and economic-healthy way, while providing choices to specialize your player-character in a field of your choosing.
Path of Survival //Each character will learn all Path of Survival Skills; Skill level is Account-Wide (shared across all characters)
Fishing
Be able to fish in all the waters of the world
Synergy Skills: Cooking, Foraging
Tools Used: Fishing rod, bait
Cooking
Prepare dishes from recipes that can be used to buff allies
Synergy Skills: Fishing, Foraging, Farming, Skinning
Tools Used: Flint and Wood, Pot, Pan
Foraging
Gather plants, herbs, seeds, and bait from forests and land
Synergy Skills: Cooking, Farming, Fishing, Alchemy
Tools Used: N/a
Path of Gathering //Each character will learn one Path of Gathering Skill; Skill level is Account-Wide (shared across all characters)
Farming
Planting seeds and harvesting crops and herbs
Synergy Skills: Cooking, Alchemy
Tools Used: Trowel, Rake, Bucket
Mining
Mining different ores and minerals from nodes
Synergy Skills: Carpenter, Blacksmith, Metalworker, Enchanter
Tools Used: Pickaxe
Logging
Cut down trees for lumber and other crafting materials
Synergy Skills: Carpenter, Farmer
Tools Used: Axe
Skinning
Skin different animals and creatures for hides and other useful items
Synergy Skills: Fishing, Cooking, Carpenter, Outfitter, Blacksmith, Metalworker, Alchemy
Tools Used: Knife
Path of Crafting //Each character will learn one Path of Crafting General Skill, specializing in one of the two related Unique Skills; Skill level is Account-Wide (shared across all characters)
Carpenter
Specialization options: Stonemason or Woodworker
Synergy Skills: Mining, Logging, Outfitter, Metalworker
Tools Used: Hammer, Saw
Outfitter
Specialization options: Tailorer / Leatherworker
Synergy Skills: Skinning, Carpenter
Tools Used: Knife, Sewing Kit, Dye Kit
Blacksmith
Specialization options: Weaponsmith / Armorsmith
Synergy Skills: Mining
Tools Used: Hammer, Anvil, Furnace
Metalworker
Specialization options: Jewelcrafter / Engineer
Synergy Skills: Mining, Skinning
Tools Used: Hammer, Anvil, Needle, Grease
Alchemy
Specialization options: Brewer / Chemist
Synergy Skills: Fishing, Cooking, Foraging, Skinning, Enchanter
Tools Used: Pot, Mortar and Pestle
Enchanter
Specialization options: Augmenter / Runecrafter
Synergy Skills: Mining, Alchemy
Tools Used: Rod, Iris Focusing Glass
Construction and Housing - Home, sweet home
Homes have an unique place in MMO games. You have really interesting systems like Runescape that allow for intricate buildings and can house all sorts of rooms and equipment, but you need to balance that with keeping people from isolating themselves. I've always liked the concept of a "building" progression system (I love Cities: Skylines for this reason!), but it needs to be remembered that you're in a shared world! I do think you should be able to escape and work on your own stuff at times, but I don't want to sacrifice that idea of "we're all in this together". With any housing system, it should be predominately focused on cosmetic systems, building consumables, and creating your own "corner" in the world.
Crafting plans unlocked from associated professions
Types of Furniture
Variety, from rugs and chairs, to beds and ceiling fans
Types of Rooms
Predominately cosmetic focused, though you could argue to have crafting rooms be allowed?
Is it an engineering limitation to have user created designs? Perhaps a creator system where people can use components to build the rooms within a specific area (Valheim comes to mind)