We have put AACC on CM successfully a couple of times in the past year. That being said there are a couple of very big limitations that have to do with SIP and the number of appearances supported (these limitations were not there in the Blue world, just a part of integration to CM). Most of those limitations (not sure if all), which are critical for many customers, are going away in the next version, 6.4. At least they are mentioned as new features in the beta software. We have also installed the AACC as a complment to Elite so the voice processing is on CM and the multimedia in on AACC.
There is no doubt the Elite and AACC have a different approach. However both are powerful in their own right, anyone who says different cannot have spent much time on one or the other. {My experience is that most people who do not like AACC have little to no actual experience with it and thus have only heard of difference, not what might be better.} I am trained on both and see the benefits of each. Because the limitations hit so many customers Avaya has backed off as an upgrade solution at this time. As I understand it that will change (again) if the next version fixes these issues. I believe long term they will get to AACC as the platform because it handles multimedia as multimedia, and the ability to perform in a SIP environment.