I feel like she is a great pick for all of the squishy damage dealers that go top... so why not just do it in mid lane? If they go double ap... go Irelia top and laugh at your screen. so once again. Why not Irelia mid?
Mid lane is for champions that scale with levels better, and top is for champions who can solo lane but need a little farm (tanks, bruisers). Part of Irelia's kit is sustain up the butt, which is great against most top laners. It doesn't do much against those who can nuke her before she can buy items (which is why she can easily beat midlaners who go top: you won't hit level 6 as fast, you can recall and get some items pre-6, teleport in, and beat them while they're still weak).
Also, she has no escape. Top lane is easier to avoid ganks in with just movement speed if you're warding properly, but mid laners typically have long-distance cc to coordinate a gank with since the jungler has less distance to cover.
Reasons.
Interesting...
The funny part is that if you prepare correctly in mid (runes, etc), you MIGHT be able to pull one off by countertrading (get harassed, jump in, stun, true dmg AA).... the risk is that you can either be blown up if you are not careful (especially if u let minions hit u too much), or after you trade you get harassed on the way back.
Still a funny lane to try... just needs more strategy I guess... 
