Sandro, also, any Karma system would require for there to be a Declaration Of Piracy mechanic, which has been discussed on these forums many time - that way the game could better distinguish between 'genuine' Piracy attempts and the CMDR Rabid Murderhobo's out there.
The two would need to be introduced together.
Not needed at all, because you cannot make the distinction between a legit "legit piracy declaration".
Pirate declares piracy, murders target anyway: free reduction in karma penalty
Increase more harsh penalties for karma kills during a piracy attempt? Well why would the pirate ever declare it?
And frankly I prefer the natural feel of ED, which was meant to be "play your way", not "piracy mode engaged. Next up: trader mode engaged..."