Will there only be gangs like Necromunda or also other kind of races? For example Necrons and Chaos? Even if not on lauch maybe later down the line as DLC? ( I have never played necromunda hence I am to young for that game)
Neither of the two you mentioned really fit in as gangs in Necromunda (particularly the Necrons). I would not be particularly surprised if we end up with Chaos as an option though, Games Workshop seems incapable of approving a license without Chaos or Tyranids in it.
Got to have Chaos, else you've ying with no yang.
In the "big games" where planets and star systems are in the balance - maybe, but Necromunda as a skirmish-level game never needed Chaos as a persistent presence to function.
If in your example, ying (yin?) means the (relative) order of the Imperium and yang the chaotic evil of... Chaos... then there's precious little "law and order" in the Underhive, and none at all in the outlands.
Necromunda has zombie outbreaks, treasure miners and bounty hunters, it has raging stereoid-chomping psychopaths vs deranged cultists (but not of the Chaos variety!) and it's a breath of fresh air compared to the sameness that is most GW licenses: Empire vs Chaos, Empire vs Orks, Empire vs Tyranids... you get the picture.