Sandbox allows you the freedom to run around and do things in whatever order you see fit and... that's just about it.
They sacrifice too much for little gain: rpg's ( or simply good video games for that matter) need restrictions. Without them, there is no real decision making and the whole thing ends up feeling...flat.
I would see Night City as massive multiple hub world you'd travel in between with your car( only one, unless you've bloody rich: you cannot steal and get away with everything (like in GTA's)). Most traversal would still be on foot( and fuel would be very much relevant).
Each hub would feel different: culture, architecture, level of danger and signify player style of progression/or his role...different roles( or more likely people with different reputation/skill sets) would find better job opportunities in different sections.
I really, really would like economy to be harsh here and with strong impact on your story and how you play.
A stranger to Night City, work your way up to higher dregs of society and you can finally buy yourself that sweet penthouse and cruise around in flying Porshe.
But with status you also have sky high expenses, you decide to skip on your security, your accounts are hacked and you end up making a few bad calls. And so you lose almost everything overnight, end up thrown in the gutters, jobs are hard to come by and you're with even less than with what you started.
Classical sandbox: run around "freely" in the world in any direction with absolutely no consequences to anything you do. Loot hundreds of dungeons, do goofy activities: whenever you want!
Cyberpunk 2077 : Economy, Progression, Player role/skills, Reputation/Social status, World locations, Quests/Jobs...all would be closely linked to one another.
Now it's a simple matter of figuring out how to make it work.
