1,2 and 6 but it's not exactly what I'd like.
My vision: street creds are the key of progression (together with eddies). It works exactly like exp. points and leveling (so we're not creating a user unfriendly system) but it's realistic.
At the beginning V is mr nobody, nobody knows him, trusts him or wants to waste his time with him. The more you complete missions the higher your reputation becomes (you gain street creds instead of exp. points), V becomes "known" and is contacted by important people like Dex De Shawn who give you more missions and so on. Side quests do the same, of course. The higher your reputation is the more vendors you unlock, meaning you can buy better gear and Cyberware (in particular illegal stuff, illegal vendors won't sell you anything if they don't trust you, you need to be in/famous to some extent as already explained in the demo). You want to buy mantis blades (high-end military grade illegal melee weapon)? You must know the right guy. With abilities fully related to cyberware in a realistic fashion street creds become the key of progression system.
Everything works like in all RPGs, nothing fancy except for the fact that you need to buy your abilities with money instead of using exp. points. I think players can handle this, we're not that stupid.
A very little detail that makes everything completely realistic.
(Shhhhh, this is a secret between me and you.... but at this point you can also remove levels from enemies since the game has an action combat system anyway and make it even more realistic. Or do we really think that you need that because players are stupid at the point they need a small number to understand that a rocket launcher deals more damage than a gun and that an heavy-armored guy with a military grade rifle is more dangerous than a street gang goon with a 9mm? All action games have this type of mechanics and progression already, even linear "very easy" games like uncharted)