I feel like her biggest issue is the free mobility. If riot makes her damage strong, then she sticks onto champions and kills them without fail. However, if her damage is really low (like it is now), then she is impossible to win lane with and works as a glorified tank in team fights.
In her rework, Riot employed the same tricks that they gave to Katarina. Now, their mobility resets more readily, so their teamfighting is more difficult to pull off, but more rewarding once the kit is mastered. However, Irelia was NEVER a teamfighting champion before her rework, and function more of as a champion who focused on winning lane, which is why so many Irelia mains abandoned her.
I think the best thing to do is give her back the early pressure, but maintain the dash resets so she isn't completely useless in teamfights.
Here are my thoughts:
PASSIVE: I think it is okay as it is now. I considered adding some healing to it (like she had with her old w), but that might stack too well with Conqueror and cause issues. If it were to be changed, I think making it function like old Aatrox passive would be cool.
**Decrease stack number to 4, and keep the attack speed and magic damage the same. NEW: Gives her healing on hit while at max stacks. However, the passive only lasts at max stacks for 3 seconds, but the duration can be slightly increased by staying in combat.**
This way, her sustain isn't overbearing and is rewarded for landing abilities.
**Q: Slight base damage increase, but no longer deals bonus damage to minions. No longer dashes through the target.**
One point of frustration with new Irelia is how she can dodge telegraphed skillshots by simply dashing to the target, which is complete bullshit and gives her extra mobility. Also, it works too well as a farming tool but sucks when it comes to damaging champions. If the healing on passive is added, then the Q healing should be removed too.
**W: Irelia can move while channeling, but it cuts her movespeed in half. Damage reduction applies to both magic and physical damage, but the channel only lasts 0.75 seconds. If Irelia blocks enough damage, she can recast this ability within 1 second to lash out, dealing damage and marking her target.**
Being a mobile champion but being completely immobile for 1.5 seconds on her ONLY defensive ability is stupid. Letting her slightly reposition will help her out, and regaining the ability to reduce magic damage will help her in laning against AP champions. Additionally, when compared to other defensive abilities like Fiora's parry, this skill is unrewarding, so now the Q reset mark and the lash when she blocks damage will reward her for using it properly. The extra mark on her W may seem unfair, but listen to the E changes first.
**E: Stun duration now scales with level. No longer marks enemy champions, instead, when it hits 1 or more enemy champions, her Q cooldown is reset**
This change aims at adding some fairness to her kit. If she E's you from a distance, then she shouldn't be able to stick on you so easily. Now, if she is already on top of you and lands an E at close range, she is able to stay in the fight for longer.
R: I think it is fine too. Shifting the power of her abilities may make her too weak or too strong, so the ultimate should be balanced accordingly.
Finally, I would like AP Irelia to still be viable.
That's all for the changes. Let me know what you think.