I’m just saying the ability could be there, but difficult for the AI to succeed. They have to sneak up and get in a perfect position behind you, not easy to do if you are aware of them. Even a time feature could be implemented; they have to be “behind” you for “x seconds” before they can attack. Basically the assassins should force you to watch your back and constantly check your 6. This increases the tension. It would be sweet to turn around and unexpectedly face a knife wielding assassin. Or to unexpectedly hear an assassin decloak directly behind you (if it makes noise), causing you to shit you pants.
Besides, I’m sure real life assassins, which the game is attempting to mimic, strive to insta-kill their targets, not play games with them and perhaps give them a chance to survive. IMO, the HL assassins should have been more difficult and deadly, but in smaller numbers.
I’d rather see the game sooner however.

and if from the above mentioned ideas any one was already posted on this website I apologice but I didn’t take the time to read all the 242 pages.