Imagine if Cassiopeia's E could crit, damage towers and be affected by attack speed

With 40CDR her E speed is faster than most late game ADCs attacks speed. It basically does crit when an enemy is poisoned so your proposed changes would just be to allow her to damage towers. Since the tower cant be poisoned it would just run her oom in my opinion and really wouldnt be all that beneficial.

So essentially an AP auto attack.