In defense of Cassiopeia's new passive...
... She really can use the new item slot, because as anyone who's played Cass can tell you, she's definitely one of the mages that makes you feel like you don't have enough inventory slots.
Think about Cassiopeia on life. You need mana sustain, so you have to rush a 
/
. Or BOTH.
But, you also need 
's because you need the slow to kite and chase and you need 
like any other mage for the MPen and you need 
to compliment her AP stacking passive and you need to buy boots 
too.
...
. You have one free item slot now, probably for a 
.
In all honestly, Riot Repertoir goes the extra mile to discuss with players sometimes about what they want in their champions. He was assigned Cassiopeia's rework, probably the toughest of the bunch considering her divided fanbase, for a reason.
Not to mention, kiting has always been core to Cassiopeia's gameplay, so the passive fits well enough.
Let's not be too hasty with our judgements now. ._.
I always just sell boots for ludens late game. Except with her old passive she would have around 1400 AP with this and still 370+ movespeed. Now she'll get decent movespeed but only like 900 AP with the same build.