What we know is from four places: Vattier, Lilayah (both members of the CDPR Community Team), the twitter page and Kyle Rowley at E3 last year. So:Street cred afaik is like reputation, it opens up new contacts and missions to you?
So Kyle Rowley told Gamespot - " ... We basically have two forms of experience. We have standard experience which you'll gain from completing core missions, and then we have what we call street cred which is an alternate experience you gain from side missions. Naturally when you're completing main quests and side quests, you kind of get a bit of both, but we king of separate and split the amount of each XP depending on if your doing a main or side mission. Main missions give core XP and side missions give the street cred. Street cred is basically a way for you to ... based on your street cred level you can unlock different vendors and will unlock fixers. So fixers are kind of like the mission givers in this world right? So they'll give you jobs to do. And you get access to new fixers as your kind of leveling up your street cred." It's around 15:30 to 16:30 in the interview.
Vattier said here on the forums - "We're not planning to introduce any reputation indicators for factions. Your reputation will be measured by a general Street Cred - reflecting how you're seen by the street. You will be able to increase it through side missions and it will allow you to unlock access to additional content, such as new shops or new missions."
Lilayah said here on the forums - "Along with a traditional XP system, players can garner Street Cred by completing side missions and jobs in the city. The player’s reputation is then used to unlock access to new vendors and contacts throughout Night City, allowing them to complete new missions."
The Twitter Account said -