Illaoi shouldn't be helpless to see a top laner leave the lane, and she should have better catch potential when she tps. A .5 second stun allocated to E (test of spirit) the moment it lands would be perfect.
I really don't think she needs a stun she does fine without but allowing it to cancel channels isn't a bad idea.
I feel that would be a bit much. She is actually really strong and can deal insane amounts of damage, and her main drawback is that she has no form of CC (outside of a slow on her E, and I guess now her tentacles). I think riot still wants to keep her to be the champion with a lot of damage but no forms of hard cc.
They'res actually a decent amount of champions who has no way to stop some one from teleporting. I'd probably rather see her E just stop channels like 
's Q then have a stun on it. Though I don't think she even needs that.
