Veigar's Event horizon

Firstly I want to state that I have nothing against Veigars rework only bit of interest.

Though I do acknowledge that against some champs this stun is highly inefective. I take it as balance team wanted to turn Even horizon into cage where veigar will torture his victim. That is nice and cool until zed jumps out and instakill the poor mage.

I am now not sure how exactly can you get from even horizon. I'd guess thatzed, leblanc and lissandra can get through. And anyone with flash, but I am not sure about that. Still If Even horizon is really meant to be torture cage then how about NO ONE can get out. Erase stun for all I care but still you cannot get out for the duration.

Its just a though and there is also question wheter any allied member of veigar could get in or deal any damage to the caged enemies (which I imagine would be pretty toxic to allies). But if this skill is about trapping enemies inside why not do just that.