Since a triple monitor configuration is a de facto standard for pro users, pro configurations, etc., I would disagree with your characterization of "three 4k" as being "amazing".

I would characterize it as the absolute bare minimum to even be in this space.

I have 5 monitors attached to my 2009 pro (3x 2560x1600 main displays, a 1920x1200 offset on the wall, and a 1920x1080 "tv" cabled out to another room) and I've considered adding a sixth.

It's hard to say how many <4k displays you can add to the ports on the back in addition to the three primary 4k displays, but it had better be more than "zero".

Are you disputing "amazing"-ness of 3 displays, or number of horizontal lines of resolution? Because I calculate your collection of displays at 7.08k, and 3 * 4k ~ 12k, or a 70% increase over your current count.

;)

Sure, but I set it up 4.5 years ago. And I didn't think it was amazing then, I thought it was just "normal".

And three (insert current high end display circa this year) monitors attached to this new mac pro will also not be amazing.

What will be amazing is if you can't add a 4th, 5th and 6th - of any resolution.

It can: take a look at Tech Specs, it's listed (for 30hz): http://www.apple.com/macbook-pro/specs-retina/

Does the Mac Pro do 60Hz 4k?

With monster FirePros it better.