Is this for real or a mockup? WOW. If they release a redesign, I'm selling my 12-Core Mac Pro, even though I don't really
need to, but want to
The fact is that the Mac Pro was neglected by Apple and in doing so, has put a chill into the Professionals whose revenue streams rely on that hardware.
In the Pro market, it becomes even more critical for a supplier to enable their customers to be able to manage their update transition timelines. Doesn't matter if we're talking about Apple and IT, or spare parts for snowblowers.
For IT applications, having to do both a hardware update and a software (OS) update simultaneously is a risk that is best to be avoided. Best Business Practices say "DON'T DO IT THIS WAY".
For Apple to offer a reasonable amount of backwards legacy support permits a customer's hardware updates to be delinked from software updates, which has benefit to the customer in reducing their risk of disruption to their business's workflow. Even with the Mac App store, Apple isn't the sole provider for all software applications, which means that it simply isn't possible today for Apple to anticipate and prevent this risk.
Spot on, everything you wrote. Many businesses are moving away from iMac's for the simple fact that if it's fried it needs to be benched for at least a couple of days (as a former Genius, iMac's are incredibly difficult to repair as the logic board rests behind everything - GPU/Cooling supplies/Power supplies/HDD's and SSD's/ODD, and of course the glass front and LED LCD panel). It is much easier to replace a graphics card or HDD/SDD in a tower such as the Mac Pro on the fly. Unless data is redundant/backed up on a server, an employee would have to either wait for a replacement iMac, or use another system in house. As well, iMac's lack the upgradability with Mac Pro's. You can get a tower to last more than the 3 years of an iMac with AppleCare by simply upgrading components.
Design and editing houses use different displays, and the iMac's don't have an option other than what is currently offered. Only the RAM is user upgradable, pretty sad. It was until three years ago that iMac's started using desktop components as well. I recall trying FCP editing on an 2009 iMac (desktop components) and even the current top i7, it's painfully slow.
Keep in mind, Steve Jobs used a Mac Pro, and for all the iDevice clamoring that's on MacRumors, HD editing and such requires a lot of time for rendering. Time=money, and I can get projects done in a fraction of the time on my 12-Core Mac Pro versus my i5 MacBook Pro.
The desktop isn't dead in a "post-PC era". I wonder how all those iOS app's are developed. On iPads?

I'd love to see an evolution of desktop systems into a "Minority Report" type setup. That would rock! I don't mind smaller form factors, but I need desktop real estate. I cannot do my work on one display, and anything smaller than 24" is difficult in some cases.