More followers, based on caps, ie, pay them daily, charisma, or reputation.
I reach a "Messiah" level in the game, I really expect to have devoted fanatical followers who will die for me.
A reputation system, so people like the Enclave and raiders know that you've killed 1,000 of their ilk and act appropriately.
Ability to buy a store, so I can become a trader and wander the wastes collecting stock for the store.
Maybe be able to purchase mercs, robots, or turrets to defend the place.
Ability to buy and deploy turrets anywhere, just like mines. Oh Joy.
When finishing the quests people's dialog does more than say "go away".
Evolution of locations.
If you dump thousands of tons of gear into a place like Megaton or Rivet City, things should evolve and improve.
I save Big Town, I reverse pickpocket armor and guns on them, and they are still miserable.
Should be able to give food and supplies to them and their attitude should adjust.
If you give 10,000 caps worth of food to Little Lamplight, Eclair shouldn't complain about not enough food to feed them.
The ability to give guns, ammo, etc to anyone that's friendly in the wasteland.
That would enable simple wastelanders to evolve from moving Deathclaw lunch to real survivors.
Getting hired as a caravan guard, or someone else's follower/protector.
Then a dialog option like "I quit" or "Take this job and shove it."
The contract killer/lawbringer perks actually having numerous missions, ie, "go here, kill these people, bring back proof".
Along with this, respawning at places like Evergreen Mills, it becomes a ghost town, such a shame because
its a great place to attack from very many different angles.
Being able upon restarting a game, to spawn from a different vault, with a different main quest.
Imagine you are a Gary clone, and you realize that you are the only one who isn't crazy, or maybe you are crazy
and go on a killing spree and find the door out.
Or you are a super mutant from vault 87!
A lycanthropy perk, at night you change into a beast! With maybe some added perception to track prey.
With this any creature/person in the wastes without "animal friend" is hostile.
A mind control perk, take control of another characters body and do things with it until they are dead or injured to some extent.
Clothing confusion. If I approach Enclave decked out in full Enclave gear, how do they know I'm hostile?
Same with raiders. To make it a bit of a challenge, factions/groups could have passwords that you
could guess at to avoid or trigger hostility.
Ghoulification and Super Mutation, as a perk (possibly quest related)
with its own benefits/disadvantages and faction interactions
caused by radiation sickness (instead of instant death).
I want to attack with radiation! Wee fun! Or evolve into an Overlord at level 30.
No level cap. XP is fun to get. Since there is a limited number of perks, then after a certain level,
be able to exchange perks, or simply adjust ranks of perks.
My own pack brahmin, with a turret!
Faction related quests that change a faction's interactions with you.
People like to RP as Enclave, the Enclave should become friendly and Brotherhood hostile.
People should notice your followers. "Wow a real super mutant", "Robots have to stay outside, their kind isn't wanted here".
Also be able to tell your followers to guard a person instead of just firing them, ie, "Hey RL-3 stick with Lucky Harith, keep him alive".
"Hey crazy cult of followers, hold Evergreen Mills from the re-spawning Raiders."
An area related notebook "Some Sewer location: hard locked door", "Some building: very hard terminal"
If I find it too early in the game I may never get back to it later.
Robot Friend, Insect Friend, Ghoul Friend and Mutant Friend perks, just like Animal Friend.
Those perks to actually work, second rank of Animal Friend and I never saw a single animal defend me.
Those perks to actually cause said creature to follow you around.
None of those creatures are friendly to each other, ah, the chaos!
Ability to cripple a foe, arrest them, and deliver them to a huge prison.
Then a giant prison break quest where you have to round up the worst of the lot that escaped.
Likewise when you are evil, Regulators that cripple you, arrest you, deliver you to the prison and you can enable the escape.
A healing dart gun, that doesn't cause hostility, so you can heal people like caravans or outscasts that are all messed up.
Finally, Fallout 4 ASAP!