this is going to be a tiny bit of a read
I would have something built on something like the Crysis 3 engine, or Dice
It would have a free roam system like skyrim preferably 1st person (built for occulus rift)
an mmo or single player experience. where each person could have hundreds of changes they can make to their character.. from how their facial hair grows in. to how their character reacts to massive groups of people.. where character traits mattered.. like, chosing introvert. would cause them to be slightly out of their element. when they cast spells they take a little longer or, they can miss (nervous twitch debuff) or something like that..but over the course of the battle ( say, 5 minutes) the debuff would go away as the character and player got immersed into the fight
a days system, where not shaving or something would give your character 5 o clock shadow.. random items like moisturizer or things of that nature could stop a character from gaining "rough hands" bonus for the "marital/dating/night time" passives. preferably something like fable where a caster would age a little faster and have scars on their hands from casting spells. unless a person purchased a random maintenance item from an npc. nothing overly pricy just enough to stop people from having massive stores of gold..
id also want to make it so that people could rob/kill npcs although this npc would cease to exist in their characters instance. and infamy would be gained in the town until either people ran from them.. or the guards would spit on them. (kind of like world of warcraft where the deathknights would have to go through the questline to be accepted by the faction.)
id also want characters to experience what we feel.. finding a generically beautiful view would give them "self satisfaction" bonus and a camera system where they could take pictures (paint,draw) of the image. or (write about it depending on the characters selected passives)
the end game would range from 5 man hard modes, to 25 man hardmodes all though all of the same gear could be gained through non repeatable quests. building blueprints. each town customized like Dark Cloud 2. where putting them in appropriate positions would change the town. this would likely be apart of a guild system. where world pvp and pve, player assistance would contribute to changes in the town. after a certain amount of players agree'd to a change via a passive notification that the town would be restructured. the guild could move it around (limitations would be npcs cant be on massively elevated or glitched platforms. i would want to go over the geodata several times to make it even and minimize /unstuck because it ruins immersion in a major way..
id want sub classes and professions like fishing,teaching,inscription,horseback riding,boating.
a player based transportation system, with npcs to back up low population servers.
where every armor in the game could be gotten in (broken,battered,unique,well kept,perfect,legendary) conditions. so someone who picked up dropped gear from a PK'er would likely be wearing permanently battered/bloodstained gear. legendary gear would be attained in pieces after raiding/mass pvping and winning by contributing to the battle (on a sliding scale based on class) to stave off afkers.
i would also want a performance type ENB. and a heavy ENB for graphically "superior" users..
the AI for the boss battles changing once a week or so. to increase the level of competition (we beat it on week 1 hard mode or things of that nature)
sorry for the massive read guys but thats my dream game...