That Edea-Griever ex-mode is real? 
Well, I agree there doesn't appear to be much thought into it, although it does kind of make sense. The Ex-mode was more about the Griever/Ultimecia fusion. I'd assume the idea would still apply, regardless of what Ultimecia is actually "wearing" xD
As for CoD, I found her design concept in Dissidia was pretty different from what she looked like in FFIII, so what the hell, they could go nuts in regards to her at this point.

Well, I agree there doesn't appear to be much thought into it, although it does kind of make sense. The Ex-mode was more about the Griever/Ultimecia fusion. I'd assume the idea would still apply, regardless of what Ultimecia is actually "wearing" xD
As for CoD, I found her design concept in Dissidia was pretty different from what she looked like in FFIII, so what the hell, they could go nuts in regards to her at this point.