Reserving judgement on the overall damage potential with the changes, given the E reset relaibility is not something you can convey with text or numbers. But it's clear that Riot wants her damage to come almost exclusively from her E. Assuming her E comes out making up for the lost damage on Q and W, the other changes have me feeling kind of underwhelmed.
The Riot posts discussing her PBE changes explicitly mentions pushing Q and W more towards utility purposes than damage ones, with the vast majority of her damage coming from E. If this is the case, given how much damage Q and W have lost, I don't feel the utility aspects have been amped enough, following that vision.
Her existing Q gives a movespeed amp of 15% to 25% with rank. PBE Q gives 10% to 30% with rank. In addition to losing damage, having a longer cooldown and casting delay, you lose 5% movespeed early and only gain 5% late. I'd think, with the new vision of Q being less about damage and more about making sure she can deal her damage, that the rank 5 number should be more like 50% movespeed. Nerf her base movespeed some if you have to, but the underlying point is that her Q is her primary way of keeping up with, or getting away from, her current target. She herself is immobile, and occupies a lane where common picks have 2 to 3 in-kit movement abilities. She needs this if we're going to see her become relevant, regardless of the new E DPS. Alternatively, have the movespeed scale with her AP by some ratio. I know that typically, this kind of scaling is only given to Supports. But then again, Kayle has it on the movespeed from her pitiful heal, and in any event is never played as a Support anyway.
Her existing W slows those afflicted by 15% to 35% with rank. PBE W slows for 15% to 45% with rank. In exchange for an extra 10% slow at max ranks, she has almost double the cooldown, haf the damage, and 1/3rd less damage from AP. Um... Not worth. Let's be honest here. The only reason someone is going to be standing in your W for more than 1 second is if they are stunned or rooted. This means that, at most, you are getting 2 seconds of damage/slow out of Miasma. That is incredibly silly.
Miasma should work more like Viktor's Gravity Field. For each second you are inside it, you get a stack. Each stack does damage and slows for a small %. Then, when you move out of it, the stacks fall off 1 at a time. What the damage would look like in that setup, I'm not really sure, given the vision of E being the majority of her damage. The slow, however, however, should be something like 6% to 9% per stack at rank 5, up to 5 stacks. Maybe higher, I don't know.
[Edit] After writing this, I see the PBE W now starts at 25% instead of 15%, meaning that in exchange for all she's giving up on W, she's gaining 10% across the board on the slow. Trade still not worth. [/Edit]
http://imgur.com/a/kjSGm Cass should have 20/20 vision and a wider angle of view at close range for her ult, including units inside her hitbox (at least the damage and slow)
I think this might be a technical limitations issue. I do kind of have to agree, her ult has a really odd area of effect given what is actually happening with it. But it would seem that it's really hard for Riot to do funky shaped hitboxes. Considering Diana's Q is the only one, and there were a lot of "complaints" from the devs once she was finally revealed about how difficult it was to make that work, and how there are still to this day things that they can't do with it... I don't see hope for a more appropriately shaped AoE for Petrifying Gaze. We may be stuck choosing between a cone and a rectangle for it.
