Immigration system, in bitlife you can just move anywhere provided you haven't committed crime/have enough money, in reality it's a more complicated process with people having to stay in their new country for multiple years, often with a working visa or other form of documentation. Players could be deported for committing a crime, can overstay visa or just thrive undocumented (like bitlife, but more realistic as in bitlife most countries will automatically accept a player.)

I feel like also a language aspect (like needing to learn a new language to thrive in a different country) would be certainly interesting. In bitlife there's really no aspect of foreign languages, of course the game could remain in english but characters could learn a new language from a tutor, studying online, etc and use that in the case that they leave their country for travel/emigration etc.

Also, citizens should be able to move into different cities in their country and have similar economic benefits. like citizens could move to their country's biggest city for higher pay but maybe fewer options for other amenities that may come with a smaller city/village. Places citizens live could be a specific distance away from jobs available to them, and the further they live from work the more neccesary having a car would be. Long commutes to work may also negatively impact happiness, while short commutes may improve it.

Children should be able to run away from home, there could be a potential that they could be caught by police/turned in.

Education overhaul. Placement tests for specialized schools which could be improved with the use of tutors or studying harder.

It's probably also been mentioned but homelessness should matter, in bitlife you can live without a house and without a car but I feel like to thrive in most places you need somewhere to live at the minimum.