I don't know why we're ignoring the current state of Irelia. She's not fun to play against when all she has to do is facemash the keyboard to pull off devastating combos that she can macro all day without watching Mana.
You can't play under turret because she can extend her stun to the stars and dive in and out of turret because it's not that hard to control the push and wait for minions.
You can pick a champ that counters her, but when a champion needs to be hard countered in order to create some kind of balance then it's a problem.
I think the healthiest way to nerf Irelia is by creating a trade-off between cooldown and costs. Irelia needs an increasing mana cost for abilities she spams, like Kass Ult. Kass Ult does increase damage, but the DoT Irelia can pour out at the cost of Mana is incredible, even before purchasing Sheen.
I think this would keep Irelia in a healthy spot, but also provide some counterplay to an otherwise braindead kit.