Ok...
let's look at this form a purely hypothetical pow...
AS in PvP requiring concealment. Part of me likes the idea. It would be fully in line with what agents are all about, IMO.
But... to make that viable, let's get the other game mechanics attuned to that idea.
1. Concealment should not be broken by a single aimed shot. Use your perception to search for us, that's what it's there for. Now if we start attacking with "ordinary" shots, that's a whole 'nother issue. But a string of AS, with the agent waiting for the next one behind his cover (concealment) should not lead to immediate detection.
2. Remove the dmg cap. This has to be done in order to balance it against multiple-specials professions, who can 40% you multiple times.
3. Give us range. Any range covered in a few strides ain't sniper range.
4. Make AS ignore AC and evades. You can't dodge what you don't know is coming, and the shot is carefully aimed at the soft spots.
5. Up the base crit mod on AS. If I aim long enough without you seeing me, and put that round in your eye, that's about as critical a hit as you'll ever get.
Or... we can just leave it as it is.
Even though I'ld love to see FC make us into the assassins we're supposed to be
Now I could expand on my realistic scenario, going on about reducing brawl distance (make all melee attacks unaffected by range enhancements). Your arms are only that long. etc.
But this was about AS, so I'll just leave it at that.