Ok, here's my ideas.
Q
Dark Flight
I like the way it works, but most people do not share the opinion. Also, the 10% health cost. Probably refund the life if it hits a champion, and apply the slow as well as the knock up. It'd let him get a few more auto's off before he has to chase them around (unless he has red buff).
W
I thought of an idea, and please tell me if it's good or not. Looking at the other ideas, it's like a short-term version of Blood of The Fallen, another idea suggested.
Bloodblade
Passive: Killing units grants a stack of Blood Thirst, granting additional stats (Ad, lifesteal, attackspeed, your choice.) Stacks fall off after (5?/15?/20?) seconds (maybe when out of battle?), and are refreshed with each kill, capping at (undecided). Large minions or monsters grant additional stacks. Champion kills temporarily grant Blood Price, applying additional damage to each auto attack equal to (% of max life? % of current life? Increased armor pen?).
Combine with Ravenous Hydra for damage in teamfights for the minions, and increased ganking potential.
Active:
Consume all stacks to deal a burst of damage (skillshot, or surrounding area) that slows and draws in an enemy. Requires at least 1(?) stack, and scales on AD and stacks consumed.
E
Now this needs huge changes. I kinda put it into Bloodblade's active, but he needs a new E.
Crimson Fury (this is my least thought out idea)
Aatrox's every auto attack increases surrounding allies attackspeed by (?%)/steals attack speed and grants it to his allies while this is active. Q is free, and heals for 10% of max life. W also heals for damage dealt (active). This is his teamfighting tool. He gets to keep his whack-the-enemy playstyle, while buffing his allies.
R
Massacre
Draws in blood from nearby enemies, doing magic damage. Then spreads out the blood to allies, increasing stats. While channeling, he puts everyone around him in stasis. Afterward, enemies are slowed by 10% for 4-5 seconds, forcing a fight. This'll increase his ability to not die after hitting enemies with Q+R. Grants AoE attacks for 5?/6? seconds afterward, and increased attack speed/AD based on however many hit. This means he'll still be able to crush enemies 1v1, as well as staying on top of them when they run. Usually, he has to chase them until his Q/E come off cooldown.
So... what do you think? When I play Aatrox, he's not the strongest teamfight, his ability more relying on jumping on enemies to 1v1, and coming out as the victor. Unfortunately, he finds it pretty hard to stay on them without red buff or frozen mallet, meaning the job is usually left half-done.