As highlighted by many of the other comments, the separation of personal and business notebooks is a deal breaker for me, and I think most of my clients. The current single interface between both your business and personal notes is fantastic, and removing that would make the tool antiquated and unusable.
As a perfect example, I currently run a "To Do" tag that shows me the tasks that I have to do for both my personal tasks, and my business tasks. Physically separating these would make the tool less efficient.
Within the Evernote Resources provided to ECC's under Talking Points, Evernote itself is highlighting its strengths as "All of your research, all in one place" and "Find what you're looking for, fast". The physical separation of personal and business notebooks is in complete opposition of Evernote's own talking points; as all your research is no longer in 1 place, and you can no longer find all your information fast as you are required to do searches across both your personal and business accounts.
Also, if you are a member of multiple business accounts, it looks like you would have a personal section and then a business section for each account; which makes this exponentially worse.