Vehicles, and a bigger wasteland. Disable fast travel.
Remove pc voice, go back to text so you can role play more. MY guy has an Arnold voice or is a gen 1 synth.
Restore attribute based dialogue choices: (Strength) How about I life you over my head and toss you to the ghouls?
TBH, googles new ai assistant tech has such believable vo, Imagine they implement that, and then all the voices are CG. Then modders could make quests with authentic endless new VO.
Allow scrapping and building anything and nearly anywhere, not designated camps
Build the default game on survival mode, and then optional classic mode where you don't need to eat/drink/sleep.
Enhance followers to have a wide range of morals, and allow player to be a proper bandit from the start, hang out with bandits, raid towns if you want. Kill anyone like new vegas.
Add karma or relationship stuff back in so you feel like a badass when your reputation precedes you, or a goody type if that is your role play.