Okay, you guys really oughta consider new Casseiopeia before deciding this is a good direction.
First of all I know she's still on the PBE, but at the moment... It's not going to matter if she does a little less damage on her AOE if she's friggin' impossible to kill lategame anyway.
For starters, buffing both the slow on W and the move speed bonus on Q means good luck catching her in a chase without using flash. Her kiting power (unless you increase her cast times) is gonna be just plain disturbing, guys..
Second, with spellvamp she was already an insane 1v1 mage, as in "I can outdps your ADC" level 1v1 mage. On live, if he ult is up, she's pretty much as much guranteed-kill-mage as Malzahar, except she can stun the whole team before instamelting you, so she's even safer. Obviously she has (a few) tradeoffs for this, but the damage is there. Giving her more damage on E and free spellvamp is a bit nuts.
Third, holy god that passive. Like, what the hell. Okay, so, unless that passive ONLY works on champions, she's going to have it maxed in lategame every game. -it gives free pseudo-spellvamp that scales with your AP on E, and it's the first unlock. Not to mention E now refunds mana (and then some) on unit kills. Yay for Swai-err... Cass. -it gives 30% free cdr. I mean wut. You buy a DFG, or WotA (and/or before then, you get blue buff) and suddenly bam. Max CDR. Some may opt to waste gold in athenes, but you could easily just get a tear instead. -free 30% your AP lategame. For Free. For playing the champ. Even badly, just playing the champ. On top of the other passive stuff.
As people have clarified in the past with reworks that seem to be out of boredom, just because they're not played often doesn't mean they need changed. Usually it ends up unbalancing them. (see, new Sona, new Xerath, etc.) Unless changes are also in place to make her ultimate not as completely teamfight changing as it is, this doesn't sound like such a good direction. Just a little warning. It seems like the goal is to make her have more single instamelt power, and frankly, with Riot's obsession with counterplay, I don't see how this fits in there. She's gonna be more than a bit strong if anything close to these numbers hit live, just throwing it out there.
Thanks for the read (and inevitable downvotes)