The 5DII severely undercut sales of the 1Ds III as the image quality of the 5DII was better
No! Have you used a 1Ds3? Do you know its DR is better than 5D2 especially in shadow? Do you consider the low ISO banding on 5D2 a better image quality?
So an early announcement like the one rumored means that the new 5D will likely be the camera many of us hope it's not; a slow focusing
It depends on what D800 announcement tells Canon about its MP and focusing ability. If the rumor is true, then D800 will still have the 51-pt AF system from D700. So if Canon's 5D3 is to compete head-to-toe, they can't put the same crappy AF from 5D2 to 5D3.
way too high (uselessly high) megapixel camera
I buy what Thom Hogan thinks (See "Amateurs Need More Pixels" on http://www.bythom.com/). Plus I think studio/landscape photogs need that camera that 1D X isn't able to answer.
that doesn't compare to the 1Dx in high ISO performance so that people who were waiting for a body with the 1Dx's features won't consider a much cheaper option in the new 5D.
People who are waiting for a body with the 1D X features are professional shooters who need those to make a living and who are comfortable paying since they are also making a good money by their photographs.
People who are waiting for a body with the 1D X features and only consider a much cheaper option, e.g. 5D3 or 7D2 are just dreaming.