you are right that he needs a new passive, but one that encourages aa'ing the enemy is not the right direction for talon. I've mentioned this before(but it got buried somewhere) but talon's q and e need the most love. his q is counter productive for a caster based assassin (aa reset is a good mechanic, but not on talon, wastes time when he has such a small window to work with) and the silence on his E is what is preventing him from receiving valuable gameplay buffs. (instant silence + gapcloser = no counterplay)
Also, the damage amps from both his passive and his E are unnoticeable at worst, and insignificant at best. (15% dmg amp = 150 bonus dmg if you already did 1k dmg. If you are already doin 1k dmg, yer target is dead reguardless, unless it's the tank, and why would an assassin target a tank?)
Here are my thoughts:
new Q "Throwing Knives":
1200 ranged point and click projectile (not skill shot).
Flies fast, does small dmg. Runs on a ammo system, allowing for the actual cast cd to be really low for spamming.
Unique property: they act like cait's ult. enemy units can body block them.
Reset mechanic: get max ammo upon killing an enemy.
Use cases: this spell will really help talon's laning phase, while giving him some valuable interaction with his lane opponent. He can use his q to last hit if struggling in lane, or he can use the range to harrass his opponent. However, the opponent is able to hide behind minions to block the projectiles and cause talon to push his lane, letting him easily over extend, thus being vulnerable to ganks. Also, when talon does all-in his target, after his main combo, he can spam his q at point blank range and as the run away for free damage and help picking up kills that might've gotten away.
Pros:
+great early game
+makes talon somewhat useful in long stalls before team fights
+great for picking off kills if initial burst wasn't enough to secure it
cons:
-low dmg per shot
-(if costs mana) could exhaust his mana pool rapidly
-possibly frustrating to play against if enemy talon gets ahead early
new E "Back Stab":
is an instant blink just like his current E
deals damage to enemy instead of silencing them
Unique property: if talon backstabs an enemy suffering from impaired movement, the cd is reset. NOTE: talon cannot backstab the same target withing a certain window(much like yasuo dash)
Use cases: by removing talon's un-interactive silence, this allows talon more counter play, and the ablity to have more damage on his kit. More damage means talon can do his job more reliably, killing squishies. Also, the reset mechanic will also allow talon the ability to out play opponents instead of being a one trick pony of jumping in, ulting, killing target, then dying due to no escape. In lane, this also opens up the option for talon to get close to the enemy to hit them with his rake first so that he can E in then E out to an enemy minion. And if talon is close to an enemy, then that means he is in their zone of control too.
new Passive "cloak and dagger": if talon receives damage that drops him below X% of his max health, talon instantly stealths for x/x+1/x+2 seconds.
due to the removal of the silence on talon's E, he now has no form of defense when he jumps head long into the enemy team. So I figured a leblanc style passive granting talon stealth would be a great idea so that if an assassination attempt goes south, that he can get out of dodge and try again later.