The death of Top lane AP Sejuani
On live, AP Sej is a viable albeit undervalued pick in the top lane. She is able to be safe or engage with her Q. Her W enables her to apply Frost to a minion wave and her E allows her to kill the minion wave. I will agree that her E allows to kill minion waves too effectively on live, I only need to put 4 points into it and I'll be able to easily get 6 cs per minion wave.
On the PBE, Sejuani's E has been overnerfed though. I understand it has a lower cooldown which will tremendously help AP Sej in teamfights and skirmishes. However it does not change the fact that she will still struggle to waveclear. And this struggle to waveclear will knock AP Sej out of viability in the top lane.
Riot, you need to reconsider your changes, I understand that you want to make Tank Sejuani a viable jungler again, but I believe that is possible without knocking AP Sejuani out of viability in the top lane.
All you need to do is add a little more base damage back to Sejuani's E. Make it 60/100/140/180/220 which is still a nerf, but then maybe compensate the base damge buff by increasing the cooldown on her E by 1 or 2 seconds but keep the scaling down on level up.
AP Sejuani Top is one of the things that I find very fun in playstyle and I wouldn't want it to be knocked out of viability if it doesn't have to be.
Also, this isn't gameplay related but I think you should rename her passive to something other than Frost, because the passive on her E says it applies Frost to the enemy which is actually quite confusing. Just name her passive Ice Armor or something similar.